f Current 


Fundamental 


Electricity 


Part  II 
Electrical  Heating 


AppliaU' 


Part  III 

Salesmanship,  Advertising  and 
Store  Management 


QUADiy 

MARK 

EDKON  ELECTRIC  APPLIANCE  COMPANY, 

CHICAGO 


EDI  SON 
SCHOOL  OF 


THE  UNIVERSITY 
OF  ILLINOIS 
LIBRARY 


t'trst  Assignment 

EDISON  SCHOOL 
o/SALESMANSHIP 


Part  I 

ELECTRICITY 


Lesson  I 

Some  Fundamentals 
OF  Electricity 


EDISON  electric  APPLIANCE  COMPANY,  Inc. 


CHICAGO 


Copyright  1921 

Edison  Electric  Appliance  Company,  Inc. 


r in  ley 


FUNDAMENTALS 


OF  ELECTRICITY 


JUST  A FEW  KEYS 

But  They  Open  to  Big  Opportunities 

Before  we  start  on  this  interesting  and  profit- 
able course  let  us  have  a brief,  informal  talk  for 
the  purpose  of  getting  clearly  in  mind  just  what 
the  careful  study  of  these  lessons  is  going  to 
mean  to  you. 

We  assume  you  are  a salesman  or  would  like 
to  become  one.  You  have  chosen  that  work  of 
your  own  accord  and  we  take  it  for  granted  that 
you  are  interested  in  making  it  pay  you  as  large 
a return  in  money  as  possible. 

You  probably  know  many  men  who  are  sales- 
men in  different  lines.  Some  are  more  efficient 
than  others;  some  are  making  more  money  than 
others.  Generally  speaking,  the  difference  in 
classes  of  salesmen  lies  in  the  measure  of  their 
knowledge  regarding  the  thing  which  they  are 
selling. 

Some  men  can  sell  anything  fairly  well.  Let 
us  take  such  a man  for  an  example.  Say  he  is 
selling  electrical  appliances.  He  will  be  a better 


4 or/"*  ' r 

‘ilO .’-  'acoJ 


EDISON  SCHOOL  OF  SALESMANSHIP 


salesman  — make  more  money — if  he  knows  thor- 
oughly his  line  of  appliances;  their  favorable 
points,  their  distinct  advantages  over  other  appli- 
ances. He  will  be  a much  better  salesman  if  he 
has  a thorough  grasp  of  the  underlying  principles 
of  salesmanship  and  of  advertising  (which  is  a 
direct  branch  of  sales  effort),  plus  a working 
knowledge  of  electricity. 

Putting  it  in  a few  words;  The  rewards  of  life 
go  to  men  who  KNOW! 

You  will  not  find  this  course  of  training  in 
salesmanship  to  be  difficult.  Electricity  is  an 
interesting  subject.  The  principles  of  salesman- 
ship and  of  advertising  are  based  largely  on 
human  nature,  and  human  nature  is  always 
interesting. 

The  only  thing  we  ask  is  that  you  go  through 
withthe  course.  There  are  only  eighteen  lessons  and 
the  time  required  each  week  is,  at  most,  only  a few 
hours  of  your  spare  time.  Once  started  on  the 
course,  enthusiastically  and  with  determination 
to  finish  it,  we  feel  sure  you  will  enjoy  the  lessons 
as  much  as  any  time  you  spend  in  reading. 

The  facts  and  principles  and  rules  that  you 
master  in  this  course  will  enable  you  to  increase  your 
selling  ability  and  to  increase  your  success  in  life. 


FUNDAMENTALS  OF  ELECTRICITY 


T to  get  the  most 

XTL\^  V V from  this  course 

Look  for  the  main  points — the  laws, 
the  principles,  the  rules  of  the  things 
studied.  These  primary  rules  are  rela- 
tively few,  and  it  will  not  be  difficult 
for  you  to  understand  them  and  to 
store  them  in  your  memory  for  use 
when  needed.  The  man  who  knows 
how  to  apply  the  principles  has  mas- 
tered the  subject. 


SOME  FUNDAMENTALS  OF 
ELECTRICITY 

What  Is  Electricity? 

Have  you  ever  considered  the  tremendous 
work  which  electricity  is  doing  in  the  world  today  ? 
Electrical  energy  drives  our  machinery,  lights 
our  houses  and  buildings,  transmits  messages 
from  one  part  of  the  world  to  the  other.  It  makes 
possible  the  automobile,  the  street  car,  the  sub- 
way and  elevated  trains. 

While  we  are  able  to  recognize  it  by  its 
properties,  to  measure  it,  and  to  harness  it  to  do 
our  work,  what  electricity  really  is,  is  not  defi- 
nitely known. 

There  have  been  many  theories  advanced. 
The  greater  part  of  these  have  been  discarded. 
But  a consideration  of  one  or  two  of  these 
theories  will  be  helpful. 

For  example,  one  theory  held  that  electricity 


s 


EDISON  SCHOOL  OF  SALESMANSHIP 


was  a fluid  which  pervaded  all  matter.  While  this 
theory  has  been  discarded  it  helps  us  to  picture 
the  nature  of  electricity. 

The  latest  theory  holds  that  “electricity  is  a 
rapid  vibration  of  the  molecules  of  the  conductor 
and  in  the  space  immediately  surrounding  the 
conductor.”  A molecule  is  one  of  the  tiny  par- 
ticles of  which  all  matter  is  composed,  and  is  the 
smallest  particle  of  matter  which  can  exist  by 
itself.  The  exact  nature  of  these  vibrations  has 
not,  as  yet,  been  determined.  It  is  assumed, 
however,  that  these  electrical  vibrations  are 
similar  to  light  and  heat,  and  travel  at  the  same 
speed  as  light;  i.e.,  186,000  miles  per  second. 

In  this  course  we  will  concern  ourselves 
especially  with  the  properties  of  electricity,  a 
knowledge  of  which  has  made  its  commercial 
application  a reality,  and  we  will  see  how  these 
properties  are  applied  in  practice. 

Electricity  Exists  in  Two  Eorms — 
Static  and  Current 

Static  Electricity 

As  early  as  the  year  600  B.  C.,  it  was  known 
that  the  rubbing  of  certain  substances  together, 
as  two  pieces  of  amber  for  example,  would  make 
them  attract  light  particles  of  matter.  It  was 
also  discovered  from  time  to  time  that  other  sub- 
stances, including  rubber  and  glass,  possessed 
this  property  of  attraction  when  they  were  rubbed 
together.  The  early  Greeks  knew  amber  by  the 


6 


FUNDAMENTALS  OF  ELECTRICITY 


name  of  “electron”  and  it  is  from  this  term  that 
the  word  electricity  was  derived. 

What  is  produced  by  rubbing  two  pieces  of 
amber,  or  rubber,  or  glass,  etc.,  together  is  a form 
of  energy  that  is  known  to  us  as  static  electricity 
or  electricity  at  rest;  i.e.,  under  restraint  but  ready 
to  discharge  itself  when  released.  Static  electricity 
is  produced  by  friction. 

The  discharge  of  static  electricity  is  noticeable 
in  two  familiar  ways.  One,  in  the  crackling  of 
the  hair  when  combed  in  very  dry  weather,  and 
the  other,  the  crackling  spark  produced  when  an 
object  is  touched  after  one  has  shuffled  one’s  feet 
across  a carpet.  Furthermore,  lightning  is  the 
discharge  of  static  electricity  which  has  been 
stored  up  in  the  clouds. 

Static  electricity,  which  is  one  form  of  elec- 
trical energy,  does  not  enter  into  the  operation  of 
electrical  appliances  commonly  used  in  the  home. 
These  operate  by  current  electricity,  which  is 
another  form. 

There  Are  Two  Kinds  of  Static  Electrical 
Charges— Positive  and  Negative 

Let  us  return  again  for  a moment  to  the  sub- 
ject of  static  electricity,  which,  we  have  found,  is 
produced  by  friction,  by  rubbing  two  substances 
together.  Static  electricity  is  either  positive  or 
negative.  Two  objects  which  are  charged  with 
positive  electricity  or  two  objects  which  are 
charged  with  negative  electricity  have  a tend- 
ency to  repel  one  another.  Objects  which  are 


7 


EDISON  SCHOOL  OF  SALESMANSHIP 


oppositely  charged  attract  one  another.  We 
find  that  if  we  take  a piece  of  glass  and  rub  it 
with  a piece  of  silk,  the  glass  will  have  z.  positive 
charge.  If,  on  the  other  hand,  a piece  of  sealing 
wax  is  rubbed  with  flannel,  the  sealing  wax  has 
a negative  charge.  This  is  because  of  the  nature 
of  the  various  substances  with  which  we  have  to 
deal;  i.e.,  their  inherent  qualities. 

Current  Electricity 

The  second  form  of  electricity  is  current  elec- 
tricity., or  electricity  in  motion.  Current  electricity 
never  exists  in  stationary  form.  It  exists  only 
when  in  motion. 

As  it  is  current  electricity  which  is  used  in 
electrical  appliances  in  the  home,  we  will  confine 
ourselves  in  this  course  to  a consideration  and 
discussion  of  this  form  only. 

What  Is  Meant  by  a Circuit 

The  path  along  and  in  which  electricity  flows 
is  known  as  a circuit.  In  flowing  over  this  path 
or  circuit  the  current  electricity  naturally  follows 
a certain  direction,  which  direction  is,  of  course, 
always  out  from  the  point  of  highest  pressure. 
In  any  device  generating  current  electricity,  there 
are  always  two  poles,  as  hereinafter  shown, 
which  are  known  as  the  positive  and  negative 
poles.  The  student  should  note  that  this  has 
nothing  to  do  with  the  positive  and  negative 
charges  which  we  have  seen  to  exist  in  static 
electricity.  In  current  electricity,  positive  and 

8 


FUNDAMENTALS  OF  ELECTRICITY 


negative  current  refer  only  to  the  direction  of 
flow  from  or  to  the  source  of  supply.  The  pole 
from  which  the  current  flows  out  is  known  as  the 
positive  pole,  or  the  pole  of  high  pressure.  The 
negative  pole  isthepole  through  which  thecurrent 
returns  to  the  source  of  supply  and  is  the  pole  of 
low  pressure.  A circuit  may  now  be  more  fully 
defined  as  that  path  over  which  the  electric  cur- 
rent flows  from  its  starting  pointy  or  positive  pole, 
out  over  its  path  and  again  back  to  its  source,  or 
negative  pole. 


Current  Electricity  — How  Produced 

Current  electricity  is  ordinarily  produced  in 
two  ways;  by  chemical  action  and  by  magnetism. 

The  most  common  example  of  current  elec- 
tricity produced  by  chemical  action  occurs  in  the 
well  known  electric  battery  used  in  operation  of 
electric  door  bells,  telephones,  telegraphs  and 


9 


EDISON  SCHOOL  OF  SALESMANSHIP 


Other  similar  devices.  These  are  known  as 
“primary”  batteries  to  distinguish  them  from 
the  “secondary”  or  “storage”  batteries. 

A primary  battery  is  a device  for  converting 
chemical  energy  directly  into  electrical  energy. 
There  are  two  kinds  of  primary  batteries,  known 
as  “wet”  and  “dry.” 

The  ordinary  “wet”  battery  consists  of  two 
pieces  or  poles  of  different  metals  (poles  gen- 
erally of  copper  and  zinc)  placed  in  a liquid 
which  acts  in  different  ways  on  these  metals.  The 
liquid  used  is  generally  diluted  sulphuric  acid  or 
a solution  of  sal-ammoniac.  When  the  metals 
are  connected  by  a wire  outside  the  liquid,  electric 
energy  is  generated  by  the  chemical  action  of  the 
acidon  themetals  and  then  flows  through  the  wire. 

The  chemical  action  which  takes  place  in  this 
conversion  of  chemical  energy  into  electrical 
energy  is  simple.  The  sulphuric  acid  attacks  the 
zinc  plate,  causing  it  to  gradually  waste  away. 
Just  as  a heated  body  will  give  off  its  heat  to  one 
of  lower  temperature,  so  also  the  zinc  plate  in 
this  process  of  consumption  caused  by  the  attack 
upon  it  of  the  sulphuric  acid  gives  off  the  elec- 
trical energy,  which  is  produced,  to  the  copper 
plate.  The  copper  plate  is  therefore,  as  will 
readily  be  seen,  continually  being  charged  with 
electrical  energy  by  the  action  of  the  solution. 
The  copper  plate  or  pole  being  of  higher  potential 
or  pressure  than  the  zinc  plate  or  pole,  continu- 
ally discharges  electric  current, which,  as  has  been 
explained,  flows  out  over  the  circuit  to  the  point 


10 


FUNDAMENTALS  OF  ELECTRICITY 


of  lower  pressure,  which  in  this  case  is  represented 
by  the  zinc  or  negative  pole. 

Thus  are  established  two  distinct  parts  of  the 
path  for  the  electric  current.  The  first,  from  the 
zinc  through  the  solution  to  the  copper;  the 
second,  from  the  copper  through  the  outside  wire, 
back  to  the  zinc.  This,  then,  is  a simple  example 
of  what  an  electric  circuit  is.  Anything  to  be 
aflFected  by  the  current  generated  in  the  battery, 
must  be  so  connected  on  the  outside  wire  before 
mentioned  that  the  current  may  pass  in  at  one  side, 
out  at  the  other  and  back  to  its  point  of  origin. 

A dry  battery  is  practically  the  same,  except- 
ing that  the  solution  exists  in  a dry  paste  form. 

The  second  method  of  producing  current  elec- 
tricity  isbymagnetism.  This  is  commercially  done 
by  means  of  the  so-called  dynamo.  The  curren  t used 
in  the  home  and  in  the  commercial  world  is  princi- 
pally produced  by  magnetism  through  dynamos. 

There  are  two  kinds  of  dynamos:  those  which 
produce  direct  current  and  those  which  produce 
alternating  current.  By  - direct 
current  we  mean  that  current 
which  flows  continually  in  one 
direction;  that  is,  it  starts  from 
one  pole  (the  “positive  pole”) 
and  flows  continually  through 
the  circuit  to  the  other  pole  (the 
“negative  pole”).  By  alternat- 
ing current  we  mean  current  Showing  how  a circuit 

- •I’ll  1 * formed  on  an  ordinary 

which  periodically  changes  its  push-bumn  beii  outfit 
direction,  flowing  first  in  one  direction  completely 


11 


EDISON  SCHOOL  OF  SALESMANSHIP 


through  the  circuit,  and  then  in  the  opposite 
direction  completely  through  the  circuit;  the  poles 
change  from  positive  and  negative  to  negative 
and  positive,  alternating  back  and  forth,  and  thus 
reversing  the  current. 

Direct  current  is  necessary  for  certain  pur- 
poses, while  alternating  current  is  necessary  or 
desirable  for  others,  and  is  the  current  most 
generally  used.  For  example,  in  electroplating  di- 
rect current  only  can  be  used;  i.e.,  current  which 
flows  constantly  in  one  direction.  For  lighting 
purposes,  on  the  other  hand,  alternating  current  is 
generally  advisable,  although  direct  is  often  used. 
This  will  be  explained  in  a subsequent  lesson. 

Referring  to  our  definition  of  alternating 
current  you  will  note  that  it  is  current  which 
continually  reverses  its  direction,  flowing  first 
forward  and  then  backward,  etc.  One  such 
complete  reversal  of  the  current,  forward  and  back- 
ward, is  known  as  a cycle.  In  some  dynamos 
producing  alternating  current  the  current  makes 
60  complete  reversals  or  cycles  each  second,  or 
makes  1 20  alternations  per  second.  This  is  known 
as  a 60-cycle  dynamo.  The  number  of  complete 
cycles  which  the  current  makes  each  second  is 
known  as  the  frequency  of  the  current.  While 
there  are  dynamos  which  produce  current  of 
other  frequencies,  those  used  for  producing 
electric  light  in  this  country  generally  have  a fre- 
quency of  60  cycles. 

The  principal  diflFerence  between  an  alternat- 
ing current  and  direct  current  dynamo  lies  in  the 


12 


FUNDAMENTALS  OF  ELECTRICITY 


fact  that  a direct  current  dynamo  has  what  is 
called  a commutator;  because,  as  a matter  of  fact, 
both  kinds  of  machines  generate  alternating 
current.  The  commutator  on  a direct  current 
machine  is  a device  by  which  the  current  is  col- 
lected and  sent  out  continuously  in  one  direction. 
The  commutator  is  a cylinder  on  the  shaft  of  the 
direct  current  generator,  composed  usually  of 
copper  segments  separated  from  each  other  by 
electrical  insulation,  revolving  under  collector 
brushes  placed  at  certain  points.  These  brushes 
are  usually  made  of  carbon  and  correspond  to 
the  positive  and  negative  poles  of  a battery. 

Alternating  current  generators  do  not  have 
commutators. 

Conduction 

In  theory,  all  bodies  conduct  electricity  to  a 
greater  or  lesser  extent.  It  follows,  therefore, 
stating  the  matter  the  other  way,  that  all  bodies 
resist  the  passage  of  electricity  to  a lesser  or 
greater  extent.  Substances  which  allow  electricity 
to  pass  through  them  readily  are  known  as  conduc- 
tors. Those  which  materially  resist  the  passage 
of  electricity  are  known  as  non-conductors  or 
insulators,  as  hereinafter  described. 

Metals  are  the  best  conductors  and  are  never 
classed  as  non-conductors  or  insulators.  In  order 
to  give  you  an  idea  as  to  the  relative  resistance  of 
different  metals,  we  will  tabulate  a few.  In  this 
table,  silver  for  a given  size  or  shape  (not  weight) 
is  shown  as  having  the  least  resistance  and,  there- 
fore, is  the  best  conductor.  For  the  purpose  of 


13 


EDISON  SCHOOL  OF  SALESMANSHIP 


comparison  we  have  taken  silver  as  “1.”  By 
referring  to  this  table,  you  will  see  that  mercury, 
though  a metal,  has  over  62  times  the  resistance 
of  silver;  or,  silver  has  more  than  62  times  the 
conductivity  of  mercury: 


Silver 

...  1.000 

Iron 

...  6.460 

Copper 

...  1.086 

Nickel 

...  7.628 

Gold 

...  1.393 

Tin 

...  8.091 

Aluminum 

...  1.935 

Lead 

...  13.050 

Zinc 

...  3.741 

Antimony  ... 

...  21.645 

Platinum 

...  6.022 

Mercury 

...  62.730 

For  commercial  purposes  copper  is  generally 
used,  as  it  is  almost  as  good  a conductor  as  silver 
and  is  much  lower  in  cost,  and  its  great  ductility 
permits  it  to  be  drawn  out  into  wire. 

Insulation  and  Insulators 


As  above  implied,  an  insulator  is  the  opposite 
of  a conductor,  being  asubstancewhich  resists  the 
passage  of  electricity.  It  is  not  possible,  however, 
to  draw  a sharp  distinction  between  conductors 
and  insulators,  as  most  substances  conduct  a 
little,  and  even  good  conductors  vary  greatly  in 
their  conductivity  or  in  the  resistance  which  they 
offer  to  the  passage  of  current  electricity. 

The  following  are  considered  among  the  best 
insulators: 

Dry  Air  Mica 

Glass  India  Rubber 

Porcelain  Silk 

Paraffin  Dry  Wood 

Vulcanite  Various  Oils 

Shellac  Chemically  Pure  Water 


14 


FUNDAMENTALS  OF  ELECTRICITY 


It  is  to  be  noted  that  ordinary  water,  being 
more  or  less  impure,  is  a conductor  of  electricity. 

Electric  light,  telephone  and  telegraph  wires 
are  supported  on  glass  or  porcelain  insulators  to 
prevent  leakage  of  the  current. 

The  choice  of  the  insulator  to  use  in  each 
instance  is,  of  course,  always  governed  by  the 
conditions  which  are  to  be  met.  For  example,  oil 
is  an  excellent  insulator  where  it  is  desired  to 
insulate  moving  parts  which  can  be  immersed  in 
the  insulating  material  itself.  It  would  obviously 
be  impossible,  however,  to  use  it  for  insulating 
wire  suspended  on  poles. 

Paraffin  is  principally  used  to  permeate  porous 
insulating  materials,  such  as  cotton,  silk  and  the 
like,  to  assist  in  preventing  leakage  of  current. 

As  an  example  of  a substance  which  is  of  par- 
ticular usefulness  as  an  insulator  we  mention 
mica.  Besides  being  a good  electrical  insulating 
material,  mica  is  capable  of  withstanding  high 
temperature.  Hence,  it  is  widely  used  in  elec- 
trically heated  appliances  for  insulating  the  heat- 
ing element  from  the  balance  of  the  appliance. 
In  addition  to  its  ability  to  withstand  high 
temperature,  thin  sheet  mica  is  a comparatively 
good  conductor  of  heat,  so  that  the  heat  generated, 
when  used  as  above,  easily  passes  from  the 
heating  element  to  that  place  in  the  appliance 
where  it  is  to  be  utilized. 


15 


PROBLEMS 

Part  I 

ELECTRICITY 

LESSON  II 


NAME 


STUDENT  NUMBER 


STREET  AND  MUMBER  OR  P.  O.  ADDRESS 


CITY  STATE 


EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 


CHICAGO 


' fo  un) 


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SNOixsaaO 


THE  PROBLEMS 

The  most  important  part  of  your  training  in.  this 
Course  is  your  work  on  the  Problems. 

When  you  work  the  problems,  you  concentrate  on 
the  most  important  points  of  each  lesson,  and  you  get 
these  points  clear  in  your  own  mind. 

Work  your  problems  on  this  Sheet,  writing  the 
answer  in  the  blank  space  under  each  question. 

Sign  your  name,  address,  business  connection, 
and  the  date,  and  mail  the  Problem  Sheet  to  us. 

We  wijl  go  over  your  answers,  correct  them,  give 
your  paper  a grading,  and  return  to  you. 

Upon  your  satisfactory  completion  of  the  course, 
you  will  be  awarded  a certificate. 

Address  your  replies  to 

EDISON  SCHOOL  0/ SALESMANSHIP 

Care  oj  EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 

5660  Taylor  Street,  Chicago 


PROBLEMS 

Part  I 

ELECTRICITY 
LESSON  II 


EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 

CHICAGO 


3.  What  is  the  unit  of  energy?  How  is  it  found ? 


4.  How  much  current  flows  when  220  volts  overcomes  a resistance  of  20  ohms  ? 


5.  Define  Watt;  Kilowatt;  KWH. 


6,  How  is  the  wattage  of  any  electrical  appliance  found? 


7.  If  an  appliance  designed  for  and  used  on  a 110-volt  circuit  is  stamped  SOO  watts,  how 
many  amperes  would  it  use  ? 


8.  If  you  connect  an  appliance,  designed  to  operate  at  100  volts,  on  a 200-volt  circuit, 
what  will  happen  and  why?  (Make  answers  brief  and  concise;  if  additional  room  is 
needed  use  space  below,  making  proper  reference  to  question  number.) 


The  man  who  puts  his  knowledge  to  the  test 
will  always  get  farther  in  life  than  those 
who  are  not  sure  as  to  just  what  they  know 


THE  PROBLEMS 

The  most  important  part  of  your  training  in.  this 
[bourse  is  your  work  on  the  Problems. 

When  you  work  the  problems,  you  concentrate  on 
:he  most  important  points  of  each  lesson,  and  you  get 
:hese  points  clear  in  your  own  mind. 

Work  your  problems  on  this  Sheet,  writing  the 
answer  in  the  blank  space  under  each  question. 

Sign  your  name,  address,  business  connection, 
and  the  date,  and  mail  the  Problem  Sheet  to  us. 

We  will  go  over  your  answers,  correct  them,  give 
y^our  paper  a grading,  and  return  to  you. 

Upon  your  satisfactory  completion  of  the  course, 
y^ou  will  be  awarded  a certificate. 

Address  your  replies  to 

EDISON  SCHOOL  of  SALESMANSHIP 

Care  of  EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 

5660  Taylor  Street,  Chicago 


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ANSWERS  TO  QUESTIONS 
Assignment  2 - Part  1. 

1.  Current  strength  (The  Ampere);  Resistance  (The  Ohm);  Pressure,  Electromotive  force,  (The  Volt). 

See  Pages  3 to  8 

2.  The  Ampere  is  the  amount  of  current  flowing  along  a wire  when  there  is  one  unit  of  pressure  overcom- 
ing one  unit  of  resistance.  It  is  that  unit  by  which  we  measure  the  strength  of  the  current,  or  the  rate  of 
flow.  The  Ohm  is  the  amount  of  resistance  that  allows  a current  strength  of  one  ampere  to  flow  when 
there  is  a pressure  of  one  volt.  The  Volt  is  that  force  v/hich  will  cause  a current  strength  of  one  ampere 
to  flow  through  a resistance  of  one  Ohm. 

See  Pages  3 to  9 

3.  The  unit  of  Electric  power,  or  rate  of  using  energy,  is  the  Watt.  Multiply  the  volts  by  amperes.  W - V 
X A. 

4.  Using  the  formula  on  Page  1 0 A = ^ and  substituting  in  this  formula  the  two  values  which  we  know  in 

order  to  find  the  third  one  which  we  do  not  know,  we  get:  220  j j 

See  Page  10 

5.  A Watt  is  that  unit  of  power  produced  when  one  ampere  flows  in  a circuit  under  a pressure  of  one  volt. 
The  Kilowatt  is  one  thousand  watts  (Kilo  - 1000).  KWH  is  the  abbreviation  of  Kilowatt-Hour  and  repre- 
sents a thousand  watts  for  one  hour. 

See  Pages  11-16 

6.  Multiply  the  volts  by  the  amperes  found  on  name-plate  to  get  the  wattage  of  an  appliance. 

See  Page  1 8 

7.  Amperes  equal  watts  divided  by  volts,  or  A = Substituting  in  the  formula,  we  get: 

Amperes  = = 4.54 

See  Page  1 8 

8.  If  we  connect  a 100  volt  appliance  on  a 200  volt  circuit,  the  appliance  will  probably  burnout  because  we 
get  four  times  the  power  or  wattage.  By  doubling  the  voltage  we  double  the  current  and  since  the  watt- 
age is  the  product  of  the  two,  we  get  four  times  the  wattage. 


See  Page  19 


Second  Assignment 

EDISON  SCHOOL 
o/SALESMANSHIP 


Part  I 

ELECTRICITY 


L,esson  II 

UNITS  OF  MEASUREMENT 


EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 
CHICAGO 


Copyright  1921 

Edison  Electric  Appliance  Company,  Inc. 


EDISON  SCHOOL 
of  SALESMANSHIP 

Part  I 

ELECTRICITY 


Lesson  II 

Units  of  Measurement 

IN  the  last  lesson  we  learned  of  the  nature  and 
of  certain  properties  of  electricity. 

In  this  lesson  we  will  deal  with  the  way  elec- 
tricity is  measured. 

It  seems  strange  that  we  do  not  know  what 
electricity  really  is,  and  yet  we  can  measure  it 
very  accurately. 

In  order  to  get  a fairly  clear  idea  as  to  how 
electricity  is  measured,  let  us  liken  the  flow  of 
electricity  to  the  flow  of  water. 

Suppose  that  you  had  a big  reservoir  of  water 
up  in  the  mountains,  and  were  studying  ways  to 
bring  that  water  down  into  the  valley  in  order 
to  irrigate  your  farm. 

The  Unit  of  Current  Strength  — 

The  Ampere 

One  of  the  first  things  you  would  have  to 
decide  would  be  how  large  a flow  you  needed. 
Whether  you  would  want  much  water  or  only  a 
small  quantity  to  be  flowing. 


3 


EDISON  SCHOOL  OF  SALESMANSHIP 


If  you  wanted  much  water,  you  would  dig  a 
large  ditch  to  carry  it.  If  you  wanted  only  a 
little  water,  you  would  dig  a small  ditch. 

In  other  words,  one  of  the  things  you  would 
have  to  decide  would  be  the  rate  of  flow  of  the 
water. 

Now,  just  as  there  can  be  a certain  rate  of 
flow  of  water  in  a ditch,  so  there  can  be  a definite 
rate  of  flow  of  electric  cu7-rent  along  a wire. 

The  RATE  OF  FLOW  of  the  current,  also  known 
as  the  strength  of  the  current,  can  be  measured. 
The  unit  of  measurement  is  called  the  ampere. 

Just  as,  with  a current  of  water,  you  can  say 
that  there  are  so  many  gallons  per  minute  com- 
ing through,  so  with  electricity  you  can  say  that 
there  are  so  many  amperes  coming  through. 

To  give  you  some  idea  of  the  amount  of 
current  an  ampere  represents:  The  ordinary 
25-watt  incandescent  Mazda  lamp  (on  the  usual 
110  volt  circuit)  has  a current  flowing  through 
it  of  about  of  an  ampere;  a 50-watt  Mazda 
lamp,  about  of  an  ampere. 

What  Makes  Current  Strength  — Pressure 
Divided  by  Resistance 

But  you  readily  see,  do  you  not,  that  the 
strength  of  any  current  depends  on  two  other 
factors — the  amount  of  pressure  behind  the  cur- 


4 


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rent  driving  it  forward,  and  the 
amount  of  resistance  in  the  path 
of  the  current,  trying  to  stop  it. 

Let  us  give  an  illustration: 


Suppose  you  have  a cur- 
rent of  water  flowing  through 
an  inch  pipe.  Then  suppose 
you  All  that  pipe  with  buck- 
shot. What  happens?  Why, 
the  current  slows  up.  Just 
as  in  our  previous  illustra- 
tion if  we  had  fllled  the  ditch 
with  stones.  The  buckshot 
is  a resistance.  In  effect,  it 
reduces  the  size  of  the  pipe. 
The  greater  you  make  the 
resistance,  the  less  current 
you  get. 

But  now  suppose  that 
you  put  a force  pump  on 
that  pipe  in  order  to  bring 
force  or  pressure  on  that 
current  of  water.  What  y; 
happens?  The  current 
increases.  The  greater 
the  pressure,  or  force,  the 
greater  the  strength  of 
your  current. 


The  man  at  the  force 
pump  can  INCREASE 
the  strength  of  the  cur- 
rent of  water  by  in- 
creasing the  pressure 


The  man  at  the  nozzle 
can  DECREASE  the 
strength  of  the  current 
of  water  by  increasing 
the  resistance  (turn- 
ing the  stop-cock) 


The  strength  of  the 
current  coming  from 
the  nozzle  is  the  result 
of  the  pressure  divided 
by  the  resistance 

The  same  formula  holds 
for  electric  currents 


5 


EDISON  SCHOOI.  OF  SALESMANSHIP 


Let  US  illustrate  this  with  a little  arithmetic: 

Suppose  you  had  a current  of  water  flowing 
through  a trough  at  the  rate  of  100  gallons  a 
minute. 

If  you  double  the  pressure  or  force  behind 
that  water,  you  will  get  2 times  100  or  200 
gallons  a minute. 

But  then  if  you  should  double  the  resistance 
of  those  200  gallons,  you  would  cut  the  current 
in  two.  You  would  have  one-half  of  200  gallons, 
or  100  gallons. 

So  here  is  the  formula  that  you  should  fasten 
in  your  memory: 

The  strength  of  the  current  equals  the  pressure 
divided  by  the  resistance.  (This  is  known  as  Ohm’s 
law). 

Electric  Resistance 

We  have  learned  in  the  first  lesson  that  sub- 
stances differ  in  the  readiness  with  which  they 
will  permit  electric  current  to  be  conducted 
along  them,  and  we  have  classified  them  as  good 
or  poor  conductors  according  to  their  ability  to 
conduct  current.  The  opposition  which  a con- 
ductor offers,  tending  to  retard  or  restrict  the  flow 
of  the  electric  current,  is  called  the  resistance. 

Resistance  Depends  Upon 
Various  Factors 

The  resistance  which  a conductor  (of  uniform 
shape)  offers  depends  primarily  upon  length  and 


6 


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the  area  of  its  cross  section;  in  the  case  of  round 
or  square  conductors,  therefore,  upon  length 
and  the  square  of  their  diameter.  (You  learned 
in  arithmetic  that  the  areas  of  squares  and  circles 
vary  as  the  square  of  their  diameters.)  For 
example,  a conductor  twenty  feet  in  length  will 
offer  twice  as  much  resistance  to  an  electric 
current  as  a conductor  ten  feet  long,  all  other 
things  being  equal.  Similarly  the  greater  the 
diameter  of  the  wire,  the  less  resistance  it  offers, 
just  as  a large  waterpipe  offers  less  resistance 
to  the  flow  of  water  than  a small  pipe. 

Although  by  illustration  we  have  compared 
electricity  to  water,  electricity  of  course,  is  not 
a liquid  and  does  not  “flow”  like  water.  But 
the  analogy  is  helpful  to  the  student. 

We  have  pointed  out  that  the  resistance  offered 
is  directly  proportional  to  the  length.  Now  then, 
the  amount  of  resistance  is  also  inversely  pro- 
portional to  the  square  of  the  diameter  of  the 
conductor.  For  example:  No.  24  wire  has  a 
diameter  of  .02  inch.  No.  30  wire  has  a diameter 
of  .01  inch  or  one  half  of  the  diameter  of  No. 
24  wire.  It  takes  39  feet  of  No.  24  copper  wire 
to  give  a resistance  of  one  unit,  but  it  takes  only 
9.7  feet  of  No.  30  wire,  or  one  fourth  as  much, 
to  offer  the  same  amount  of  resistance.  In 
other  words  by  halving  the  diameter  of  a wire 
we  increase  the  resistance  four  times.  So  we 


7 


EDISON  SCHOOL  OF  SALESMANSHIP 


see  that  the  larger  the  wire,  the  less  resistance 
it  offers  to  the  current. 

The  amount  of  resistance  offered  by  a wire 
depends  also  upon  the  material  of  which  it  is 
made.  For  example;  only  2.2  feet  of  No.  24 
nickel-silver  wire  will  offer  a resistance  of  one 
unit,  whereas  it  takes  39  feet  of  No.  24  copper 
wire  to  give  the  same  resistance.  Copper  is  the 
best  commercial  conductor;  hence,  wires  for 
carrying  electric  current  are  almost  universally 
made  of  copper. 

Temperature  (of  the  conductor)  also  is  a 
factor  in  the  resistance  offered.  Of  this  we  will 
speak  in  a later  lesson. 

The  Unit  of  Resistance—  The  Ohm 

The  unit  of  resistance  is  called  an  ohm,  and 
one  ohm  may  be  defined  as  the  amount  of  resist- 
ance that  allows  a current  strength  of  one  ampere 
to  flow  when  there  is  a pressure  of  one  volt.  (The 
resistance  of  a copper  wire  one  and  one-fifth  inch 
long  and  one-thousandth  of  an  inch  in  diameter, 
is  about  one  ohm.  The  resistance  of  528  feet  of 
iron  wire  one-third  of  an  inch  in  diameter  is  also 
about  one  ohm.) 

In  many  instances  resistance  is  an  undesir- 
able factor  as  it  retards  electric  current  and  uses 
up  power;  but  we  shall  see  as  we  progress  that 
it  is  largely  because  of  resistance  that  we  can 

8 


UNITS  OF  MEASUREMENT 


develop  the  heat  which  is  the  necessary  factor  in 
all  electrical  heating  appliances.  We  merely  call 
this  point  to  your  attention  here  and  will  treat 
of  it  more  fully  in  a later  lesson. 

The  Unit  of  Electrical  Pressure— 

The  Volt 

The  driving  force  which  produces  a flow  of 
electricity  is  known  as  the  electromotive  force. 
It  is  electrical  pressure,  just  as  we  speak  of 
water  pressure.  The  unit  of  electromotive  force, 
or  pressure,  is  known  as  a volt.  The  volt  accord- 
ingly may  be  considered  as  the  unit  by  which 
electrical  pressure  is  measured.  It  is  defined  as 
that  force  which  will  cause  a current  strength  of  one 
ampere  to  flow  through  a resistance  of  one  ohm. 

So  that  you  may  obtain  an  idea  of  about 
how  much  electric  pressure  a volt  is,  we  might 
mention  that  the  electric  pressure  in  the  ordinary 
dry  battery  runs  from  1.1  to  1.5  volts  and 
that  the  usual  lighting  circuit  in  this  country 
operates  at  110  volts.  In  many  foreign  coun- 
tries the  lighting  circuit  operates  at  220  volts. 

There  Is  a Definite  Relation  Between 
the  Units  of  Measurement 

You  remember  the  formula  that  we  gave  a 
few  paragraphs  back — “The  strength  of  the 
current  equals  the  pressure  divided  by  the  resis- 
tance.” 


9 


EDISON  SCHOOL  OF  SALESMANSHIP 


Now  let  US  express  this  in  electrical  terms,  as 
follows : 


Amperes  Equal  the  Volts  Divided 
By  the  Ohms 

Or,  if  we  let  “A”  stand  for  amperes,  “V”  for 
volts,  and  “O”  for  ohms,  we  may  express  this 
relation  bv  the  following  equation: 

a!y 

o 

or,  if  we  say,  A = 4,  V = 160,  and  O = 40,  then 

we  have—  160  (volts) 

4 (amperes)  = ^ ^ 

40  (ohms) 

But  if  4= then  it  is  also  true  that  4 x 40=160. 

40 

Using  the  same  arithmetical  rule  with  our 
letters,  we  can  sav  that  if  A = — then  A x O = V, 

HO  V ' o 

and  U=  ^ • 

A 


As  a practical  illustration  take  the  standard 
6-pound  Hot  Point  or  6-pound  Edison  electric 
flatiron,  110  volts: 

Amperes  (volts)  ^ ^ 25  (approx.) 

21.1  (ohms) 

From  these  equations  you  will  see  that  if 
two  of  the  three  units  are  known,  the  third  is 
easily  found  by  substituting  the  figures  known 
in  the  equation  and  then  solving  for  the  un- 
known quantity. 

For  example,  let  us  assume  that  we  have  a 
pressure  of  150  volts  and  a resistance  of  30  ohms 


10 


UNITS 


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MEASURE  M ENT 


The 

The 

The 

The 

Ampere 

Volt 

Ohm 

Watt 

: 'll.. 


Measuring  the  Electric  Current 
The  four  units  of  measurement 


and  desire  to  find  the  current  which  is  flowing 
in  amperes.  Substituting  the  known  quantities 

in  the  equation  we  find  that  A=  or  A=5. 

30 

In  other  words,  there  are  5 amperes  of  current 
flowing. 

Again,  let  us  assume  that  we  have  a current 
strength  of  7 amperes  and  a resistance  of  20 
ohms,  and  we  wish  to  find  the  amount  of  pres- 
sure in  volts.  Applying  our  formula  again  we 

find  that  ^ 

V=  7x20  or  V=  140 

In  other  words  the  electrical  pressure  is  140 
volts.  And  so  in  every  instance  where  two  units 
are  known,  the  third  is  easily  found. 

The  Unit  of  Power— The  Watt 

We  have  now  considered  the  measurement 
of  electrical  flow,  pressure  and  resistance,  which 


11 


EDISON  SCHOOL  OF  SALESMANSHIP 


we  have  learned  are  measured  by  units  known 
as  the  ampere,  the  volt,  and  the  ohm,  respective- 
ly. There  is  another  factor  the  measurement  of 
which  is  highly  important — power,  or  rate  of 
doing  work.  The  unit  of  measurement  of  electrical 
■power  is  known  as  the  watt,  just  as  the  unit  of 
mechanical  power  is  the  horsepower;  746  watts 
is  equivalent  to  one  horsepower. 

Let  us  get  clearly  in  mind  this  question  of 
rate  of  doing  work,  or  activity,  or  power,  of 
which  a watt  is  the  measure. 

Rate  of  work  is  found  by  dividing  the  work 
done  by  the  time  consumed  in  the  process. 

The  expression  “Sixty  miles  per  hour”  ex- 
presses a rate  of  speed;  you  do  not  know  how 
far  the  train  will  go  or  how  long  it  will  take  — 
you  only  have  the  rate.  It  takes  an  engine  of  a 
certain  power  to  pull  a certain  length  of  train 
at  that  rate  of  speed.  The  power  represents 
the  rate  of  doing  work;  the  actual  amount  of 
energy  expended  or  work  done  in  making  the 
trip  may  be  measured  by  the  coal  used  up  or 
the  steam  used,  or  something  else. 

Now  we  will  come  back  to  a hydraulic  anal- 
ogy. A current  or  stream  of  water  is  capable 
of  running  a water  wheel  or  a water  motor  and 
doing  work.  Its  power,  or  rate  of  doing  work, 
depends  on  the  “strength”  of  its  current  (i.  e., 


12 


UNITS 


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MEASUREMENT 


the  amount  of  flow  in  a given  time),  and  its 
“force”  as  measured  by  its  pressure  or  head. 

Suppose  you  lived  somewhere  where  there 
was  no  electricity  and  you  connected  a water 
motor  to  your  kitchen  faucet  to  run  a washing 
machine.  There  would  be  a certain  flow  from 
the  faucet  which  is  under  a certain  pressure,  say 
50  pounds  per  square  inch,  and  you  get  a certain 
power,  or  rate  of  doing  work.  Now,  if  you  had 
a larger  faucet  and  feed  pipe,  you  would  get  a 
larger  flow  and  you  would  expect  more  power 
or  a faster  rate  of  work.  Or,  if  you  kept  to  the 
original  faucet  but  the  town  water  pressure  was 
increased,  you  would  also  expect  more  power. 
The  -power  would  he  proportional  to  both  the  flow 
and  the  pressure. 

So  the  power,  or  rate  of  doing  work,  in  an 
electric  circuit  depends  upon  the  same  two 
factors;  First,  the  strength  of  flow,  or  amperage; 
Second,  the  electric  pressure,  or  voltage.  In 
fact,  the  electric  power  is  the  product  of  these 
two  factors. 

A watt  then  is  that  unit  of  power  produced 
when  one  ampere  flows  in  a circuit  under  a pressure 
of  one  volt. 

The  watts  may  accordingly  be  found  by 
simply  multiplying  the  volts  by  the  amperes  as 
expressed  in  the  following  equation: 

W = V X A 


13 


EDISON  SCHOOL  OF  SAI,  ESMANSHIP 


For  example:  a standard  6-pound  Hotpoint 
or  Edison  flatiron  is  rated  at  110  volts  and  5 3^ 
amperes.  Then  the 

Watts  = V (110)  X A (534)  = 575  (approx.) 

The  corresponding  flatiron  intended  to  be 
used  on  a 220  volt  circuit,  which  is  common  in 
foreign  countries,  would  be  rated  at  2^  am- 
peres. And  the  product  of  the  volts  and  the 
amperes  in  this  case  would  be  220  x 2^  = 605 
watts  — which  gives  approximately  the  same 
product  and  wattage  as  that  of  the  110  volt  iron. 

The  Watt-Hour 

We  have  been  dealing  with  a measure  of  the 
rate  of  doing  work, — the  unit  of  power  which 
is  the  watt.  We  need  now  to  have  a measure 
of  the  work  actually  done,  or  the  electrical  en- 
ergy expended,  and  this  introduces  the  factor 
of  time  — the  work  done  as  measured  hy  the  length 
of  time  the  power  is  applied. 

If  we  apply  a watt  of  power  for  one  hour,  we 
have  a unit  of  work  done  which  is  called  the 
watt-hour.  The  watt-hour  may  be  defined  then 
as  the  equivalent  of  one  watt  used  for  one  hour. 
It  may  be  only  a half-watt  used  for  two  hours, 
or  two  watts  used  for  only  one-half  hour;  in 
fact,  any  combination  that  equals  one  watt  for 
one  hour. 


14 


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It  is  easy  to  understand  that  two  watts  ap- 
plied for  one-half  hour  will  do  the  same  work 
as  one  watt  applied  for  one  hour,  just  as  two 
men  might  unload  a carload  of  coal  on  a siding 
in  one-half  day,  and  one  man  would  do  the 
same  job  in  a whole  day.  The  work  done  would 
be  the  same  in  both  cases. 

If  H equals  hours,  or  the  length  of  time  the 
power  is  applied,  then 

WH  = WxH 

or  the  power  multiplied  by  the  length  of  time. 

We  have  seen,  however,  that  the  power  W 
is  the  product  of  the  pressure  and  the  current, 
or  the  volts  times  the  amperes.  Therefore 
WH  = V X A X H 

which  is  saying  that  the  work  done,  or  the 
energy  expended,  depends  on  the  length  of  time 
that  a current  is  applied  under  a certain  pressure. 

To  illustrate:  An  appliance  of  4 amperes 
110  volts  (like  a Hotpoint  or  Edison  Toaster) 
consumes  440  watts,  that  is,  its  rate  of  using 
power;  if  operated  for  one  hour,  it  uses  440  watt- 
hours;  for  one-half  hour,  220  watt-hours;  for  two 
hours,  880  watt-hours  — that  is,  watt-hours  is 
the  measure  of  the  work  done. 

For  example: 

WH  =V(=110)xA(=4)xH(=  1)  =440 
WH  = V ( =110)  X A ( =4)  xH  ( =3/^)  =220 
WH  = V ( = 110)  X A ( =4)  X H ( = 2)  =880 


IS 


EDISON  SCHOOL  OF  SALESMANSHIP 


A watt  is  a measure  of  the  rate  of  doing  work. 
A watt-hour  is  the  measure  of  energy  actually 
expended,  or  amount  of  work  done. 

The  Kilowatt-Hour 

In  commercial  practice  we  do  not  use  the 
watt-hour  to  measure  electrical  energy,  because 
it  is  so  small.  We  have  accordingly  adopted  a 
unit  of  measurement  which  is  1000  watt-hours, 
called  the  kilowatt-hour,  expressed  KWH. 

The  word  kilo  means  1000  and  so  the  kilo- 
watt-hour is  a thousand  watts  for  one  hour,  or 
250  watts  for  four  hours,  or  2000  watts  for 
one-half  hour,  or  one  watt  for  1000  hours;  or 
any  combination  which  is  the  equivalent  of  1000 
watts  for  one  hour.  This  will  explain  what  is 
meant  when  a bill  for  electricity  reads  18  KWH 
@ 10c  = 31.80. 

A kilowatt-hour  or  a thousand  watts  applied 
for  one  hour  will  operate  for  one  hour,  forty  25- 
watt  Alazda  Lamps,  or  two  electric  flatirons,  or 
a one  horsepower  motor. 

But  a kilowatt-hour  will  also  operate  for  one- 
half  hour,  eighty  25-watt  Mazda  Lamps,  or  four 
electric  flatirons,  or  a two  horsepower  motor. 

To  go  further,  a kilowatt-hour  will  operate 
for  six  minutes,  four  hundred  25-watt  Mazda 
Lamps,  or  twenty  electric  flatirons,  or  a ten 
horsepower  motor. 


16 


UNITS  OF  MEASUREMENT 

The  cost  of  operating  will  be  the  same  in  all 
three  cases  because  the  quantity  of  work  done, 
or  energy  consumed,  is  the  same — one  kilowatt- 
hour.  The  Electric  Lighting  Company  sells 
KWH — k i lo  wa  tt-hou  r s . 

But  the  power,  or  rate  of  doing  work,  neces- 
sary in  the  last  case  would  be  ten  kilowatts,  in 
the  second  case  it  would  be  two  kilow’atts,  and 
in  the  first  case,  as  already  stated,  it  would  be 
one  kilowatt. 

Examples  of  Wattage 

You  may  easily  apply  what  you  have  learned 
about  watts  by  observing  the  markings  on  the 
name  plates  of  electric  appliances.  Sometimes 
the  amperes  and  volts  are  given,  but  usually  the 
watts  and  volts  are  given. 

In  the  first  instance,  if  a name  plate  on  the 
appliance  is  marked  “5  amperes  110  volts,”  then 
you  get  the  watts,  of  course,  by  multiplying 
5x110,  which  will  give  you  550.  Usually  the 
manufacturers’  catalogs  give  the  wattage  and  in 
this  way  you  can  check  the  ratings  with  the 
published  information. 

The  modern  tendency,  however,  is  to  mark 
the  watts  directly  on  the  name  plate  because 
that  is  what  the  user  is  most  interested  in.  The 
amperes  were  formerly  marked  for  the  benefit 
of  the  electrician,  who  wanted  to  know  the  size 


17 


EDISON  SCIIOOI.  OF  SALESMANSHIP 


To  find  the  wattage  of  any  electric  appliance 
marked  with  amperes  and  volts  use  the  following 
method: 


AMPERES  X VOLTS  = WATTS 


For  example: 


3 AMPERES  X 110  VOLTS  = 330  WATTS 


Therefore,  such  an  appliance  will  con- 
sume 330  watt-hours  of  electricity  if 
operated  continuously  for  one  hour 


of  wire,  which  is  determined  by  the  amount  of 
current  and  not  by  the  wattage.  However,  if 
a name  plate  is  marked  “600  watts  and  110 
volts,”  then  if  we  wanted  to  find  the  amperes, 
our  rule  would  be  to  divide  the  wattage  by  the 
volts  according  to  the  formula: 


and  in  this  case  A would  equal  5.45  amperes. 


While  the  voltage  is  always  marked  on  a 
name  plate,  we  might  have  some  case  where  we 
have  the  watts  and  the  amperes  and  wanted  to 
find  the  volts.  The  formula  would  then  be: 


A 


and  if  the  watts  were  600  and  the  amperes  6,  of 
course,  the  voltage  would  be  100. 

Another  practical  point  is  brought  out  by 
what  we  have  learned  about  wattage.  If  you 


18 


UNITS  OF  MEASUREMENT 

take  an  appliance  marked  110  volts  and  con- 
nect it  on  a 220-volt  circuit,  such  as  is  occa- 
sionally found  in  this  country,  you  get  four  times 
the  power  or  wattage  and  will  probably  destroy 
the  article. 

The  resistance  remains  constant,  because  it 
is  a definite  quality  of  the  design  of  the  appli- 
ance, but  doubling  the  voltage  also  doubles  the 
current  which  flows  through  the  appliance — and 
the  wattage  is  the  product  of  the  two — hence  you 
get  four  times  the  wattage. 


Now  that  you  have  finished 
Lesson  Two,  lay  down  the  papers 
for  a moment  and  review  in  your 
mind  what  you  have  read.  Recall 
the  three  fundamental  measurements 
of  electricity,  the  ampere,  the  ohm, 
the  volt.  What  do  each  of  these 
represent.^  Go  over  the  lesson 
mentally  as  far  as  possible.  Then 
take  up  the  lesson  again,  and  be 
sure  you  have  not  missed  any  of 
the  important  principles,  particularly 
those  which  are  in  italics  — they  are 
the  key  to  the  whole  lesson.  Now 
you  are  ready  to  answer  the  question 
sheet. 


19 


• s, 


PROBLEMS 

Part  I 

ELECTRICITY 

LESSON  I 


EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 

CHICAGO 


oStoiqa  ‘was  JojXex  °99i 

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s 


Part  I 


ELECTRICITY 


LESSON  I 


EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 


CHICAGO 


QUESTIONS 


1.  What  is  the  latest  theory  of  the  nature  of  electricity  ? 


2.  What  are  the  two  forms  of  electricity  ? How  do  they  differ  from  each  other? 


3.  How  is  current  electricity  produced  ordinarily  ? 


4-  Describe  the  formation  of  an  electric  current  by  a battery.  What  are  the  two  kinds  of 
primary  batteries  and  how  do  they  differ  ? 


5.  What  are  the  two  kinds  of  current  electricity  ? 


6.  What  IS  a cycle  ? What  is  meant  by  60-cycle  current  ? 


7.  What  is  a conductor  ? An  insulator  ? 


8.  What  is  an  excellent  insulating  material  for  the  heating  elements  of  electrically  heated 
appliances?  Why? 


9.  Name  some  good  conductors  and  some  good  insulators. 


i >, 


- "> 

I 'fySw,  X?:  '."'tl  bri/''’'.':;  •»;!'■ » 


Form  335-5221 


EDISON  SCHOOL  OF  SALESMANSHIP 

5600  West  Taylor  Street 
CHICAGO,  ILL. 


1. 


2. 


3. 


4. 


5. 


6. 


7. 


8. 

9. 


ANSWERS  TO  QUESTIONS 


Assignment  1 - Part  1 

The  latest  theory  of  nature  of  electricity  is  that  it  is  a rapid  vibration  of  the  molecules  of  the  conduc- 
tor and  in  the  space  immediately  surrounding  the  conductor. 

See  Page  6 - Paragraph  2 

Static  electricity,  which  is  electricity  at  rest  produced  by  friction,  and  current  electricity,  which  is  elec- 
tricity in  motion. 

See  Page  7 - Paragraph  2 

Current  electricity  is  ordinarily  produced  in  two  ways;  by  chemical  action  and  by  magnetism. 

See  Page  9 - Paragraph  2 

When  the  two  poles  of  the  ordinary  "wet"  battery,  placed  in  a solution  of  sal-ammoniac  or  diluted 
sulphuric  acid,  are  connected  by  a wire  outside  the  liquid,  electric  energy  is  generated  by  the  chemi- 
cal action  of  the  acid  on  the  metals  and  then  flows  through  the  wire,  (b)  The  dry  battery  is  practi- 
cally the  same  as  the  wet  battery  except  that  the  solution  exists  in  a dry  paste  form. 

See  Page  1 0 - Paragraph  3;  also  Page  1 1 - Paragraph  2 

Direct  current  flows  continually  in  one  direction;  it  starts  from  the  positive  pole  and  flows  continually 
thru  the  circuit  to  the  negative  pole.  Alternating  current  periodically  changes  its  direction,  flowing 
first  in  one  direction  completely  through  the  circuit,  and  then  in  the  opposite  direction  completely 
through  the  circuit. 


See  Page  1 1 - Paragraph  4 

One  complete  reversal  of  alternating  current  in  a dynamo  forward  and  backward,  is  known  as  a cycle. 
In  some  dynamos  producing  alternating  current,  the  current  makes  60  complete  reversals  or  cycles 
per  second,  or  makes  1 20  alternations  per  second.  This  is  a 60-cycle  dynamo. 

See  Page  1 2 - Paragraph  3 

Substances  which  allow  electricity  to  pass  through  them  readily  are  known  as  conductors.  Those 
which  materially  resist  the  passage  of  electricity  are  known  as  non-conductors  or  insulators. 

See  Page  1 3 - Paragraph  3 

Mica;  It  is  capable  of  withstanding  high  temperature  and  is  a good  conductor  of  heat. 

See  Page  1 5 - Paragraph  5. 

Good  conductors:  Copper,  silver,  gold,  aluminum- 

Good  insulators:  Dry  air,  glass,  porcelain,  mica. 


Third  Assignment 

EDISON  SCHOOL 
of  SALESMANSHIP 


Part  I 

ELECTRICITY 


Lesson  III 

The  Cost  of  Operation  and 
Its  Measurement 


EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 

CHICAGO 


Copyright  1921 

Edison  Electric  Appliance  Company,  Inc. 


PROBLEMS 

Part  I 

ELECTRICITY 

LESSON  III 


STUDENT  NUMBER 


STREET  AND  NUMBER  OR  P.  O.  ADDRESS 


EDISON  ELECTRIC  APPLIANCE  CO.,  Inc. 


CHICAGO 


fo  }pimi  uo  pinuituoo  suoiu>nb  fo  }ftj) 


ilsoo  aija  aq  ]jia\  jBqM  ‘KM'S 

sjuaa  01  XjpujDaja  qjiyW  ^‘auiu  siqa  Suunp  pauinsuoa  uaaq  SBq  XiTouioap  qontu 
AVOH  spesJ  IJ  ^epoj^  '£9SZ  Jajaui  upuaD  v jo  Suip^aj  aqi  oSb  qaaM  auQ  ’j 


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SNOiisaaO 


-i 


The  man  who  puts  his  knowledge  to  the  test 
will  always  get  farther  in  life  than  those 
who  are  not  sure  as  to  just  what  they  know 


PROBLEMS 

Part  I 


THE  PROBLEMS 


ELECTRICITY 


The  most  important  part  of  your 
training  in  this  Course  is  your  work  on 
the  Problems.  ■ 

When  you  work  the  problems,  you 
concentrate  on  the  most  important  points 
of  each  lesson,  and  you  get  these  points 
clear  in  your  own  mind. 

Work  your  problems  on  this  Sheet, 
writing  the  answer  in  the  blank  space 
under  each  question. 

Sign  your  name,  address,  business 
connection,  and  the  date,  and  mail  the 
Problem  Sheet  to  us. 

We  will  go  over  your  answers,  correct 
them,  give  your  paper  a grading,  and 

Upon  your  satisfactory  completion  of 
the  course,  you  will  be  awarded  a 

Address  your  replies  to 


LESSON  III 


EDISON  SCHOOL  of  SALESMANSHIP 

Care  of  EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 


EDISON  ELECTRIC  APPLIANCE  CO.,  Inc. 


3.  If  the  hand  on  the  “Hundreds”  dial  in  the  illustration  in  this  lesson  (page  7)  had  been 
as  it  is  now,  but  the  hand  on  the  “Tens”  dial  had  pointed  between  0 and  1,  what  would 
have  been  the  reading  of  the  meter? 


4.  An  electric  iron  has  a wattage  of  575.  A week’s  ironing  takes  three  hours,  but  the 
plug  was  out  one-third  of  the  time.  How  much  does  it  cost  to  do  the  ironing  with 
electricity  at  10  cents  per  KWH? 


5.  A 110-volt  toaster  takes  4 amperes  and  toasts  two  slices  of  bread  on  both  sides,  in  5 
minutes.  What  will  be  the  cost  of  toasting  20  slices  of  bread  on  this  toaster  with  elec- 
tricity at  10  cents  per  KWH? 


6.  An  electric  coffee  percolator  consumes  440  watts  and  makes  6 cups  of  coffee  in  fifteen 
minutes.  How  would  you  express  the  cost  of  operating  the  percolator  to  the  customer 
and  why? 


7.  If  the  electric  meter  should  happen  to  be  inaccurate,  in  which  direction  would  the  dis- 
crepancy usually  be? 


The  man  who  puts  his  knozvled^e  to  the  test 
will  always  get  farther  in  life  than  those 
who  are  not  sure  as  to  just  what  they  know 

THE  PROBLEMS 

The  most  important  part  of  your 
training  in  this  Course  is  your  work  on 
the  Problems. 

When  you  work  the  problems,  you 
concentrate  on  the  most  important  points 
of  each  lesson,  and  you  get  these  points 
clear  in  your  own  mind. 

Work  your  problems  on  this  Sheet, 
writing  the  answer  in  the  blank  space 
under  each  question. 

Sign  your  name,  address,  business 
connection,  and  the  date,  and  mail  the 
Problem  Sheet  to  us. 

We  will  go  over  your  answers,  correct 
them,  give  your  paper  a grading,  and 
return  to  you. 

Upon  your  satisfactory  completion  of 
the  course,  you  will  be  awarded  a 
certificate. 

Address  your  replies  to 


EDISON  SCHOOL  of  SALESMANSHIP 

Care  of  EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 

5660  Taylor  Street,  Chicago 


, .If  iOii'r 

; xri  y 


Jvr, 


\ 


Edison  School  of  Salesmanship 

5600  WEST  TAYLOR  STREET 

CHICAGO,  ILL. 


ANSWERS  TO  QUESTIONS 
3- 

Assignment  # - Part  1 . 


The  meter  registers  the  amount  of  electricity  used  in  KWH  Kilowatt  Hours. 


By  subtracting  2563  from  2574,  we  get  1 1 KWH  which  is  the  amount  of  current  used.  If 
we  multiply  1 1 (KWH)  by  the  cost  of  electricity  per  KWH,  or  10  cents,  we  get  $1.10. 

2380. 


575  watts  X 2 hours  =1150  watt  hours.  1 1 50  watt  hours  = 1.15  KWH. 
1.15  KWHx  10  = 11.5. 


110x4  = 440  watts.  20/2  = 10  X 5 = 50  minutes  = 5/6  of  1 hour. 

440  watts  X 5/6  = 366  watt  hours.  366  KWH  x 10  cents  = 3.66  cents. 

400  X . 1 0 = 04  cents  = cost  of  operation  for  one  hour,  1 5 minutes  or  1 /4  hour  at  .04  cents 
an  hour  = .0 1 cost  of  making  six  cups  of  coffee.  Operation  cost  is  most  effectively  express- 
ed to  a customer  by  saying  "one-sixth  of  a cent  per  cup"  rather  than  by  saying  "24  cups  per 
hour  at  a cost  of  4 cents.  In  addition  to  being  better  selling  psychology,  this  more  closely 
expresses  the  actual  cost  of  operation. 


The  meter  will  register  less  than  has  been  used. 


EDISON  SCHOOL 
of  SALESMANSHIP 

Part  1 

ELECTRICITY 


Lesson  III 

The  Cost  of  Operation  and 
Its  Measurement 


DO  you  know  how  to  read  an  electric  meter? 

Do  you  know  how  to  calculate  the  cost 
of  operating  any  electrical  appliance  for  any 
given  length  of  time? 

These  are  points  which  may  come  up  any 
time  during  your  efforts  to  make  a sale.  Some- 
times sales  are  lost  simply  because  the  questions 
a prospective  buyer  asks  can  not  be  answered 
instantly  and  with  conviction.  Suppose  a wom- 
an at  whose  home  you  called  to  make  a sale 
said:  “My  bills  for  electricity  are  very  unrea- 
sonable. I don’t  know  how  the  company 
figures  them,  but  I know  I do  not  use  as  much 
current  as  the  company  charges  me  for.  How 
do  they  figure  those  bills  ?”  Could  you  answer 


3 


EDISON  SCHOOI,  OF  SALESMANSHIP 


her  satisfactorily?  Could  you  take  her  to  the 
electric  meter  in  her  home  and  show  her  how 
to  figure  her  own  bills? 

Let  us  take  another  point.  Suppose  during 
the  process  of  making  a sale  on,  let  us  say,  an 
electric  iron,  the  prospective  purchaser  said: 
“Yes,  that  may  be  a good  iron,  but  I am  told 
they  take  a lot  of  current.  I am  afraid  it  would 
be  too  expensive  to  operate.” 

Could  you  figure  for  that  woman  the  exact 
cost  of  operating  the  appliance  during  an  hour’s 
ironing?  And  could  you  do  it  in  a way  that 
would  convince  her? 

These  are  the  important  points  covered  by 
this  lesson.  Let  us  first  take  the  electric  meter. 

The  Electric  Meter 

(Watt-hour  Meter) 

We  have  learned  what  very  definite  units 
there  are  by  which  electricity  may  be  measured; 
and  that  the  watt  hour,  or  rather,  the  kilowatt 
hour,  is  the  measure  by  which  electricity  is  sold. 
(KWH  = Kilowatt  hour  =1000  watt  hours.)  It 
measures  the  energy  used,  which  is  in  exact  pro- 
portion to  the  work  done  by  the  electric  current. 
The  various  units  of  measurement  of  electricity 
can  be  very  accurately  recorded  in  commercial 
instruments,  or  meters. 


4 


THE  COST  OF  OPERATION  AND  ITS  MEASUREMENT 


In  this  lesson  when  we  speak  of  the  “meter,” 
we  will  refer  only  to  the  watt-hour  meter,* 
which  is  the  meter  installed  and  connected  in 
all  premises  that  are  wired  for  electric  service. 

In  principle,  the  electric  meter  is  really  only 
a small  electric  motor  driving  a set  of  dials,  the 
motor  being  so  designed  as  to  revolve  at  a speed 
exactly  proportional  to  the  amount  of  electric 
energy  being  used. 

In  the  standard  type  of  meters,  the  speed 
of  the  motor  is  regulated  by  a horizontal  metal 
disc  which  revolves  on  jewel  bearings  between 
horseshoe  magnets.  Most  meters  are  marked 
with  the  value  in  watt  hours  for  each  revolution 
of  the  disc.  This  figure  may  be  found  on  the 
name  plate  or  marked  on  the  disc. 

In  most  types  you  can  see  this  disc  revolve. 
For  example  assume  that  one  revolution  of  disc 
measures  one  watt  hour.  If  one  watt  of  elec- 
tricity were  being  used,  the  disc  would  revolve 
once  an  hour.  When  a 50-watt  Mazda  lamp  is 
being  used,  the  disc  will  make  50  revolutions  in 
an  hour.  Or,  if  the  lamp  were  on  for  one- 
fiftieth  of  an  hour,  the  disc  would  revolve  once 
and  the  meter  would  register  one  watt  hour,  or 
one  one-thousandth  of  a kilowatt  hour  (KWH). 


*NOTE: — There  are  ether  meters  for  measuring  electricity,  such  as  Ammeters,  or 
Ampere  meters,  for  measuring  the  flow  of  current;  Voltmeters  for  measuring  the  pres- 
sure, or  voltage;  Wattmeters  for  measuring  the  rate  of  power  used,  etc. 


5 


EDISON  SCHOOL  OF  SALESMANSHIP 


(Such  a very  small  amount,  of  course,  could  not 
actually  be  observed  on  the  dials  of  the  ordinary 
meter.) 

Thus  the  moment  an  electric  lamp,  or  any 
other  current-consuming  appliance  connected 
on  the  circuit  is  switched  on,  this  little  motor 
begins  to  revolve,  and  at  a speed  in  keeping 
with  the  wattage  consumption  of  the  appliance 
or  appliances  connected  on  the  circuit. 

This  motor  has  no  work  to  do,  except  to 
revolve  the  metal  disc  referred  to,  and  to  move 
the  little  hands  on  the  dials  of  the  meter,  which 
leave  a record  of  the  exact  amount  of  electricity 
consumed. 

Accuracy  of  Electric  Meter 

It  is  because  this  motor  (unlike  motors  for 
operating  sewing  machines,  washing  machines, 
etc.)  has  practically  no  work  to  perform,  that 
it  can  be  very  delicately  and  accurately  made, 
and  the  weight  of  its  rotating  part  is  so  small, 
and  the  bearings  so  delicate,  that  no  measurable 
amount  of  energy  is  consumed  in  operating  it. 

One  peculiarity  of  the  electric  meter  is  that 
only  dust  and  friction  are  at  all  likely  to  affect 
its  accuracy,  and  both  of  these  necessarily  have 
a retarding  effect,  causing  it  to  register  less  cur- 
rent than  has  been  used.  The  chances  of  its 
registering  more  are  remote  indeed. 


6 


THE  COST  OF  OPERATION  AND  ITS  MEASUREMENT 


Meters  in  use  in  residences  are  often  tested 
in  large  numbers,  and  it  is  exceedingly  seldom 
that  one  is  found  that  is  appreciably  inaccurate. 

How  to  Read  a Meter 

Let  us  now  turn  to  the  dials  of  the  meter 
and  learn  to  read  them,  and  be  able  at  any  time 
to  determine  how  much  electricity  has  been 
consumed  in  a given  period.  The  meter  is  made 
to  read  in  kilowatt  hours. 


2 3 8 6 


A meter  usually  has  four  dials,  as  illustrated 
above.  The  dial  at  the  right  registers  from  one 
to  ten,  the  units;  the  hand  on  this  dial  moves 
from  one  number  to  the  next  for  each  KWH 
and  makes  a complete  revolution  for  every  ten 
kilowatt  hours. 

The  second  dial  from  the  right  indicates  the 
tens,  and  its  hand  moves  from  one  number  to 
the  next  for  each  ten  kilowatt  hours  used,  and 
makes  a complete  circle  for  every  one  hundred 
kilowatt  hours. 


7 


EDISON  SCHOOL  OF  SALESMANSHIP 


The  third  dial  from  the  right  registers  the 
hundreds,  and  the  dial  at  the  left,  thousands. 

The  little  figures  above  the  dials  indicate 
the  complete  quantity  which  each  dial  registers. 
For  example:  We  have  stated  that  the  second 
dial  from  the  right  measures  tens,  while  the 
figure  above  the  dial  is  “100.”  This  means  that 
the  dial  will  measure  ten  for  each  division  and 
100  when  the  hand  goes  completely  around  the 
circle. 

When  the  hand  is  approaching  0,  it  is  ap- 
proaching 100  in  value;  when  it  is  leaving  0, 
it  is  leaving  zero  in  value;  the  hand  on  the  next 
dial  to  the  left  — the  hundreds  hand  — has 
moved  around  to  the  next  figure  and  added  a 
hundred  more  to  the  meter  record,  so  that  the 
tens  hand  begins  at  zero  again,  and  starts  re- 
cording tens  to  make  up  the  next  hundred. 

So  with  the  units  hand:  it  measures  up  to 
ten,  and  the  instant  it  touches  0 it  measures 
zero  again,  and  starts  to  record  the  next  ten. 
The  ten  just  measured  is  now  recorded  by  the 
tens  hand. 

To  read  the  meter,  it  is  only  necessary  to 
write  down  the  numbers  registered  on  the  dials, 
writing  them  in  the  same  order  as  the  dials  on 
the  meter,  and  always  taking  the  smaller  of 
the  two  numbers  between  which  each  hand 
points.  We  have  applied  this  to  the  illustra- 


8 


THE  COST  OF  OPERATION  AND  ITS  MEASUREMENT 


tion  (page  7)  and  placed  the  number  below  each 
dial,  showing  that  the  meter  registers  2386. 

Sometimes  the  hand  on  the  dial  will  appar- 
ently rest  directly  over  the  figure  and  yet,  in 


Because  the  hand  on  the  right- 

— you  know  that  the 
hand  on  the  left-hand 
dial  has  NOT  passed 

hand  dial  has 
NOT  passed  O 

2,  and  should  be  read 
as  1 

/Tf'Yx 

8) 

1 V G 

l3  7J 

\7  3/ 

some  cases,  the  next  smaller  figure  should  be 
used.  Take  the  following  illustration: 

When  a hand  is  on  top  of  a number  (as  in 
the  dial  shown  at  the  left  above)  do  not  put  down 
that  number  unless  the  hand  on  the  dial  to  the 


Because  the  hand  on  the 

—you  know  that 
the  hand  on  the 
left-hand  dial  has 
passed  2 

right-hand  dial 
has  passed  O 

8' 

1 r i H 

l3  7; 

' V7  3 

RIGHT  of  it  has  passed  0.  If  it  has  not,  put 
down  the  next  lower  number. 


9 


EDISON  SCHOOL  OF  SALESMANSHIP 


You  will  readily  understand  why  this  is. 
For  instance,  on  any  dial  (except  the  one  at  the 
extreme  right  end,  of  course)  the  hand  travels 
only  one-tenth  as  fast  as  the  hand  on  the  dial 
to  its  right.  Because  of  this  slower  movement, 
it  is  almost  impossible  to  tell  whether  the  hand 
has  actually  passed,  or  not  quite  passed  the 
number  it  rests  over.  You  will  readily  see  that 
in  the  case  of  the  third  dial  from  the  right  (page 
7)  any  error  in  judging  the  position  of  the  hand 
would  mean  an  error  of  100  kilowatt  hours. 

But  in  every  case,  even  should  the  hand  be 
slightly  misplaced,  and  actually  have  passed  the 
center  of  the  number  over  which  it  is  found,  you 
can  definitely  determine  which  number  to  put 
down  by  noting  the  position  of  the  hand  at  the 
right  of  it. 

There  is  another  point  about  reading  a meter 
which  must  now  be  brought  out;  that  is,  the 
registration  on  the  dials  of  the  meter  gives  a 
record  of  the  total  kilowatt  hours  since  the 
meter  started  from  zero. 

Take  the  meter  dials  in  the  illustration  on 
page  7 which  show  that  2386  KWH  have  passed 
through  the  meter  since  the  meter  started  from 
zero.  Let  us  assume  for  illustration  that  the 
average  family’s  consumption  of  electricity  is  30 
kilowatt  hours  a month  (if  we  assume  the  lighting 
rate  is  10  cents  per  kilowatt  hour,  this  would 


10 


THE  COST  OF  OPERATION  AND  ITS  MEASUREMENT 

represent  a bill  of  i53.00  per  month).  In  this 
meter,  then,  we  have  the  total  kilowatt  hours 
consumed  by  such  a family  for  793^2  months,  or 
more  than  six  years.  This  meter  will  register 
until  10,000  kilowatt  hours  have  been  used,  when 
it  will  continue  to  register  but  starting  over 
again  from  zero. 

If  we  now  assume  that  the  meter  man  has 
just  visited  a residence  where  this  meter  is  in- 
stalled, he  will  put  down  in  his  book  the  reading, 
2386  kilowatt  hours.  The  next  time  he  comes 
around  to  read  the  meter  we  will  assume  that 
the  dials  then  read  2417,  which  will  show  that 
31  kilowatt  hours  have  been  used  during  the 
month.  In  other  words,  IT  IS  THE  DIFFER- 
ENCE in  monthly  readings  that  is  paid  for. 


In  Meter  Reading 
It  Is  Only  the  Difference 
That  Counts 


//,  at  one  readin^y  the  meter  dials 
register  23H(),  and  if  one  month  later 
they  are  found  to  register  239S,  then 
the  amount  of  electricity  consumed  for 
the  month  is  239H  — 2386  or  J2  KWH 


To  find  out  how  much  electricity  has  been 
used  then,  it  is  necessary  to  take  two  readings — ■ 
at  the  beginning  and  at  the  end  of  the  period 


II 


EDISON  SCHOOL  OF  SALESMANSHIP 


which  it  is  desired  to  measure;  it  may  be  an 
hour,  a day,  a week,  or  a month. 

We  have  learned  that  the  reading  of  the 
meter  at  any  one  time  has  nothing  to  do  with 
the  current  consumed.  Whether  a new  meter 
which  may  be  installed  registers  36  or  4628  is 
of  no  significance,  as  it  is  always  the  difference 
between  two  readings  which  represents  the  con- 
sumption of  electricity. 

It  is  accordingly  on  this  difference  as  shown 
on  the  meter  readings  that  the  lighting  company 
bases  its  bills. 

How  to  Determine  the  Electricity  Used 
Or  the  Wattage  of  an  Appliance 

If  it  is  desired  to  determine  either  the  watt- 
age of  a lamp  or  of  an  appliance,  or  the  electricity 
used  in  a given  time,  it  is  only  necessary  to  con- 
nect such  lamp  or  appliance  on  a circuit  to  which 
a meter  is  connected  and  operate  it  over  a given 
period  of  time. 

Suppose  you  wanted  to  know  the  amount  of 
electricity  consumed  by  a standard  Hotpoint  or 
Edison  flatiron,  you  would  first  make  sure  that 
there  were  no  lights  or  other  electric  appliances 
connected  in  the  house.  You  can  check  this  by 
looking  at  the  meter  and  observing  that  the 
revolving  disc  on  the  meter  is  stationary.  You 


12 


THE  COST  OF  OPERATION  AND  ITS  MEASUREMENT 


would  then  switch  on  your  electric  flatiron  and 
make  a note  of  the  time  and  the  reading  on  the 
meter  dials. 

Let  us  assume  that  the  meter  reading  is 
2386  kilowatt  hours.  Let  us  suppose  that  you 
continued  ironing  two  hours,  and  that  part  of 
this  time  the  current  was  turned  off  to  prevent 
the  iron  from  becoming  too  hot.  At  the  end  of 
this  time  you  would  read  the  meter  and  might 
find  that  it  registered  2387  KWH,  which  would 
show  that  the  flatiron  had  consumed  one  KWH 
during  the  period  of  two  hours’  ironing.  (In 
this  test  only  the  hand  on  the  dial  on  the  right 
end  would  have  moved  perceptibly;  i.  e.,  from 
6 to  7;  the  hand  on  the  next  dial  would  have 
moved  only  one-tenth  as  much;  and  the  hand 
on  the  third  dial  one  one-hundredth  as  much, 
and  of  course,  could  not  be  observed.)  If  you 
had  used  the  iron  for  only  one  hour,  you  would 
have  used  only  one-half  KWH. 

If  the  current  had  been  on  the  flatiron  during 
the  whole  time,  for  two  hours,  the  actual  reading 
would  have  been  1.15  KWH  (1150  watt  hours). 
Now  then,  if  we  want  to  know  the  wattage 
rating  of  the  flatiron  we  would  take  the  watt 
hours  consumed  for  one  hour  and  this  would 
give  us  575  watts,  which  in  fact,  is  the  reading 
on  the  name  plate  of  the  flatiron. 


13 


EDISON  SCHOOL  OF  SALESMANSHIP 


To  find  the  wattage  of  an  appliance  by  means 
of  the  meter,  it  is  only  necessary  to  have  it  reg- 
ister continuously  on  the  meter  for  one  hour.,  in 
which  case  the  reading  changed  into  watt  hours 
is  the  measure  of  watts. 


If  the  electrical  appliance  is  operated  more 
than  an  hour,  take  the  reading  in  kilowatt  hours 
and  change  it  into  watt  hours  and  divide  by 
the  number  of  hours  the  device  is  in  operation. 
In  the  case  of  the  flatiron  just  referred  to  we 
said  that  the  meter  reading  would  be  1.15  KWH 
in  a period  of  two  hours,  therefore 

1.15x  1,000 

=b/b  watts. 


In  such  cases  the  current  must  be  on  contin- 
uously. 


Determining  the  Cost  of  Operation 

When  we  have  the  meter  readings,  we  find 
the  cost  of  operation  by  multiplying  the  KWH 
by  the  rate  charged  per  KWH. 

Throughout  this  course  we  will  assume  the 
rate  charged  by  the  Lighting  Company  to  be  10 
cents  per  KWH,  which  makes  easy  figuring  (and 
as  a matter  of  fact,  is  the  rate  usually  charged 
for  lighting  purposes).  It  must  be  pointed  out, 
however,  that  some  companies  have  to  charge 
more,  while  some  can  charge  less,  and  some  small 


14 


THE  COST  OF  OPERATION  AND  ITS  MEASUREMENT 


companies  and  those  which  operate  for  a short 
season  of  the  year  have  to  charge  15  and  20  cents 
per  KWH,  and  even  more. 

Many  companies  make  a special  rate  for 
electric  cooking  of  3,  4 or  5 cents  because  it  is 
“OFF  PEAK”  business,  somewhat  on  the  same 
principle  that  a lower  charge  is  made  for  a 
matinee  compared  with  an  evening  show. 

In  the  previous  lesson  we  have  learned  how 
to  find  the  wattage  from  the  name  plate  mark- 
ings on  an  electrical  appliance,  and,  when  we 
have  the  watts,  to  find  the  watt  hours  by 
multiplying  the  watts  by  the  hours  the  appli- 
ance is  in  use,  or  rather,  the  hours  the  electricity 
is  actually  flowing  through  it.  From  this  we  can 
estimate  or  determine  the  COST  of  operation  by 
multiplying  by  the  rate  charged  per  KWH — in 
all  our  lessons,  assumed  to  be  10  cents. 

Let  us  take  a few  more  illustrations: 

Mazda  lamps  are  rated  in  watts.  There- 
fore, if  a Mazda  lamp  is  marked  25  watts  you 
will  know  that  in  one  hour  this  lamp  consumes 
25  watt  hours  or  14o  kilowatt  hours  (25  divided 
by  1000).  Therefore  such  a lamp  would  need 
to  burn  40  hours  to  consume  one  kilowatt  hour 
of  electricity. 

Again  consider  a Hotpoint  electric  radiator 
stamped  600  watts.  Such  a radiator  will  accord- 


15 


EDISON  SCHOOL  OF  SALESMANSHIP 


ingly  consume  or  % kilowatt  hours  in  one 

hour.  With  electricity  at  10  cents  per  KWH 
the  cost  of  operating  this  radiator  would  be 
% X 10  or  6 cents  per  hour. 

Many  appliances,  in  place  of  being  stamped 
in  watts,  have  the  voltage  at  which  they  are 
designed  to  operate  and  the  amperage  which 
they  require  stamped  on  them.  As  has  been 
previously  pointed  out,  to  find  the  wattage  of 
such  an  appliance  it  is  only  necessary  to  multi- 


Electric  iron 

MADE  BY 

' Blank  Electric  Mfg. Co. 

AMPERES  W3M  VOLTS  fTSl 


Illustration  of  name  plate  on  a 3-lb.  electric  iron 


To  find  the  wattage  multiply  amperes  by  volts: 
3 amperes  x 110  volts=330  watts  or  amount  of 
current  iron  will  consume  if  operated  contin- 
uously for  one  hour 


ply  the  number  of  volts  by  the  number  of  am- 
peres. For  example,  a three-pound  electric  iron 
stamped  110  volts  3 amperes  would  have  a 
wattage  of  330  watts  per  hour  or  approximately 
Vs  KWH  per  hour.  With  the  cost  of  current  at 
10  cents  per  KWH  the  cost  of  operating  this  iron 
would  be  3^  3 cents  per  hour  if  the  current  were 
on  continuously. 

It  should  be  here  pointed  out,  however,  that 
this  would  not  be  a correct  result  for  the  cost 


16 


THE  COST  OF  OPERATION  AND  ITS  MEASUREMENT 


of  Operating  such  an  iron  for  one  hour  even 
though  our  figures  as  to  the  wattage  of  the  iron 
are  correct.  The  reason  why  it  cannot  be  stated 
definitely  that  the  cost  of  operating  the  iron  in 
the  foregoing  example  is  cents  per  hour  is 
that  this  assumes  that  the  current  remains 
turned  on  during  the  entire  hour. 

In  many  electrically  heated  appliances  the 
current,  however,  is  not  flowing  during  the 
entire  time  that  the  appliances  are  in  use,  nor 
is  it  desirable  to  have  it  flowing  continuously. 
The  actual  cost  of  operating  them  therefore  is 
considerably  less  than  would  appear  from  simply 
figuring  the  amount  of  current  used  per  hour 
when  continuously  connected  to  the  circuit. 

In  the  case  of  well-designed  6-lb.  irons  it  is 
not  necessary  to  keep  the  current  turned  on 
continuously  while  the  iron  is  being  used.  In 
ordinary  practice  the  iron  woidd  be  disconnected 
for  about  one-third  of  the  time.  The  actual  cost 
of  operation  would  then  be  about  3^  cents  per 
hour  and  not  5^  cents. 

Again:  a good  coffee  percolator  with  a 
wattage  of  say  400,  nominally  consumes  4 cents 
worth  of  electricity  per  hour  when  the  rate  is 
10  cents  per  KWH.  This  cost  is  insignifi- 
cant, however,  when  it  is  realized  that  in  a 
percolator  of  this  class  it  is  possible  to  make 


17 


EDISON  SCHOOL  OF  SALESMANSHIP 


six  cups  of  coffee  in  15  minutes  or  less,  and  that 
therefore  the  cost  of  current  is  but  one  cent  for 
six  cups. 

This  is  an  important  factor  to  remember  in 
the  selling  of  electrical  appliances.  Six  cups  of 
coffee  for  one  cent — makes  a far  better  impres- 
sion upon  the  prospective  purchaser,  and  also 
very  much  better  expresses  the  actual  cost  of 
operating  the  appliance,  than  to  name  the 
amount  it  would  cost  to  operate  it  for  an  hour. 


18 


THE  COST  OF  OPERATION  AND  ITS  MEASUREMENT 


Use  the  information  you  have 
gained  in  this  lesson  at  the  very  first 
opportunity.  Put  it  to  work.  That 
is  the  way  to  get  the  most  out  of 
this  course.  Use  it. 


Fourth  Assignment 

EDISON  SCHOOL 
of  SALESMANSHIP 


Part  I 

ELECTRICITY 


Lesson  IV 
ABOUT  Circuits 


EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 


CHICAGO 


Have  the  utmost  confidence  in 
yourself  and  in  the  electrical  goods 
you  are  selling.  Keep  in  mind  at  all 
times  that  you  cannot  accom.plish 
anything  in  greater  measure  than 
the  measure  of  your  confidence  in  it. 
This  is  true  no  matter  what  your 
ability,  your  education  or  your 
knowledge  of  electrical  appliances. 
Success  comes  more  certainly  to  the 
salesman  who  believes  in  himself 
and  in  his  firm  and  in  the  goods  he  is 
selling. 


Copyright  1921 

Edison  Electric  Appliance  Company,  Inc. 


PROBLEMS 

Part  I 

ELECTRICITY 

LESSON  IV 


NAME 


STUDENT  NUMBER 


STREET  AND  NUMBER  OR  P.  O.  ADDRESS 


CITV 


STATE 


EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 


CHICAGO 


jsaouBijdde  auioij  jEDuioap  ui  ajqnojj  asnso  ji  saop  Avojq  pjc  uk  si  •£ 


•jojFjauaS  gqi 

oj  5jDBq  puB  uiaisXs  B qSnojqj  jno  JoaBjauaS  aqi  uiojj  qaBd  jEauiaap  ub  Xyauq  aoBij^  'Z 


^ uado  II  SI  uaq^w  ^‘pasop  it  si  uaq^  jiinajp  auiaaja  ub  si  aBqy\\  'i 


SNOiisaaO 


The  man  who  puts  his  knowledge  to  the  test 
will  always  get  farther  in  life  than  those 
who  are  not  sure  as  to  just  what  they  know 


PROBLEMS 

Part  I 


THE  PROBLEMS 


The  most  important  part  of  your 
training  in  this  Course  is  your  work  on 
the  Problems. 

When  you  work  the  problems,  you 
concentrate  on  the  most  important  points 
of  each  jesson,  and  you  get  these  points 
clear  in  your  own  mind. 

Work  your  problems  on  this  Sheet, 
writing  the  answer  in  the  blank  space 
under  each  question. 

Sign  your  name,  address,  business 
connection,  and  the  date,  and  mail  the 
Problem  Sheet  to  us.  . 

We  will  go  over  your  answers,  correct 
them,  give  your  paper  a grading,  and 

Upon  your  satisfactory  completion  of 
the  course,  you  will  be  awarded  a 

Address  your  replies  to 


ELECTRICITY 

LESSON  IV  ^ 


EDISON  ELECTRIC  APPLIANCE  CO.MPANY,  Inc. 


EDISON  SCHOOL  of  SALESMANSHIP 

Care  of  EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 
5600  West  Taylor  Street,  Chicago 


CHICAGO 


4.  Write  an  essay  of  one  hundred  words  or  not  more  than  two  hundred,  on  short  cir- 
cuits. Use  only  those  facts  that  are  of  interest  to  women  customers. 


5.  There  are  how  many  kinds  of  electric  circuits  from  the  standpoint  of  wiring.?  Name 
and  illustrate  each  one. 


6.  Illustrate  the  connections  of  a Hotpoint  three-heat  grill.  Explain  how  LOW,  MEDIUM 
and  HIGH  heats  are  obtained. 


7.  What  is  meant  by  voltage  drop? 


. 8.  Name  four  types  of  circuits  usually  used  in  cities  and  the  voltage  that  each  employs. 

How  is  high  voltage  changed  to  low  voltage  so  that  it  can  be  used  in  ordinary  residence 
wiring? 


9.  What  is  the  advantage  of  a three-wire  system? 


10.  Tell  briefly  how  injury  can  come  from  electric  shocks. 


The  man  who  puts  his  knowledge  to  the  test 
will  always  get  farther  in  life  than  those 
who  are  not  sure  as  to  just  what  they  know 

THE  PROBLEMS 

The  most  important  part  of  your 
training  in  this  Course  is  your  work  on 
the  Problems. 

When  you  work  the  problems,  you 
concentrate  on  the  most  important  points 
of  each  lesson,  and  you  get  these  points 
clear  in  your  own  mind. 

Work  your  problems  on  this  Sheet, 
writing  the  answer  in  the  blank  space 
under  each  question. 

Sign  your  name,  address,  business 
connection,  and  the  date,  and  mail  the 
Problem  Sheet  to  us. 

We  will  go  over  your  answers,  correct 
them,  give  your  paper  a grading,  and 
return  to  you. 

Upon  your  satisfactory  completion  of 
the  course,  you  will  be  awarded  a 
certificate. 

Address  your  replies  to 

EDISON  SCHOOL  of  SALESMANSHIP 

Care  of  EDISON  ELECTRIC  APPLIANCE  COMPANY,  Inc. 

5600  West  Taylor  Street,  Chicago 


Edison  School  of  Salesmanship 


5600  WEST  TAYLOR  STREET 


CHICAGO,  ILL. 
ANSWERS  TO  QUESTIONS 


Assignment  4 - Part  1 . 

1.  An  electric  circuit  is  a conducting  path,  along  which  electric  current  flows  from  the  source  through  the  wires  and 
appliances  which  make  up  the  path,  back  to  its  starting  point.  A closed  circuit  is  a complete  and  continuous  con- 
ducting path.  An  open  circuit  is  a circuit  which  has  a break  or  gap  in  it,  preventing  the  current  from  flowing. 

See  Pages  3,  4,  7. 

2.  The  current  leaves  the  generator  at  the  power  station,  travels  over  an  insulated  wire,  suspended  from  poles  insulated 
with  glass  or  porcelain  insulators,  through  the  meter,  through  the  appliances,  and  finally  through  second  wire  to  its 
source  in  power  house. 

See  Pages  5,  6,  7. 

3.  An  arc  is  a break  in  a wire.  Arcing  trouble  in  electrical  home  appliances  are,  for  instance,  a broken  filament  in  an 
incandescent  lamp,  a broken  conductor  in  a flexible  cord,  a melted  fuse,  a break  in  the  wire  composing  the  heating 
element  of  an  appliance,  etc. 

See  Pages  8,  9. 


4.  This  answer  may  best  be  put  in  student’s  own  words.  Points  that  should  be  touched  upon  are:  1 . Explanation  of 
a short  circuit.  2.  Need  of  careful  insulation  to  prevent  short  circuits.  3.  Accidental  short  circuits.  4.  Paitial 
short  circuits.  5.  Grounded  circuits. 

See  Pages  9,  10,  II,  12.  . 


5.  Series  and  multiple  circuits.  In  series  circuit,  exactly  the  same  uniform  current  flows  through  the  entire  circuit.  In 
multiple  circuits,  the  current  flows  in  parallel  branches  and  divides  itself  into  these  branches  in  proportion  to  their 
relative  conductivity. 

See  Pages  1 4,  20. 

See  illustrations  Pages  1 4 and  22. 

6.  See  Pages  1 5 and  2 1 of  the  text. 

7.  Voltage  drop  is  the  loss  of  voltage  due  to  the  resistance  overcome  in  performing  work. 

See  Pages  16,  17,  18,  19  and  20. 


8.  Series  circuit,  trolley  or  street-car  power  circuit,  power  circuit  for  factories,  and  incandescent  lighting  circuit 
See  Page  24. 


High  voltage  is  changed  to  low  voltage  for  use  in  ordinary  residences  by  means  of  transformers. 
See  Pages  27  and  28. 

9.  Three  wire  system  reduces  cost  of  local  distribution  system. 

See  Page  28 


10.  Injury  resulting  from  electric  shocks  usually  occurs  in  connection  with  high  voltage  conductors.  Bad  bums  often  result 
but  injuries  are  not  usually  fatal  except  where  heart  failure  is  induced. 

See  Pages  30  and  31. 


EDISON  SCHOOL 
0/ SALESMANSHIP 


Part  I 

ELECTRICITY 


Lesson  IV 
About  Circuits 


IN  this  lesson  we  will  discuss  some  of  the 
important  facts  and  principles  of  Electric 
Circuits.  We  will  consider  them  in  a brief  prac- 
tical way,  from  the  standpoint  of  the  electric 
appliance  salesman.  The  following  sections 
will  contain  an  outline  study  of:  Complete  or 
Closed  Circuits,  Open  Circuits,  Short  Circuits, 
Voltage  Drop,  Distribution  Systems,  and  Shocks. 

The  Complete  or  Closed  Circuit 

An  electric  circuit  is  a conducting  path  (usu- 
ally a metallic  wire)  along  which  electric  current 
flows  from  the  source  through  the  wires  and 


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EDISON  SCHOOL  OF  SALESMANSHIP 


appliances  which  make  up  the  path,  back  to  its 
starting  point. 

Now  refer  to  our  previous  analogy  of  elec- 
tricity and  the  flow  of  water.  A break  in  a pipe 
will  not  stop  the  water  from  flowing,  but  a break 
in  the  wire  path  will  prevent  electricity  from 
flowing. 

In  other  words,  in  order  to  have  any  flow  of 
electricity,  we  must  have  a complete  and  con- 
tinuous conducting  path. 

If  a wire  breaks,  and  an  air  gap  is  formed,  the 
electric  flow  stops.  You  will  remember  that  in 
our  first  lesson,  dry  air  was  placed  at  the  head 
of  the  list  of  insulators. 

It  is  interesting  to  note  here  that  it  takes 
at  least  1000  volts  to  jump  an  air  gap  of  1/20  of 
an  inch,  and  20,000  volts  or  more  to  jump  one 
inch.  Think  of  the  immense  voltage  of  a 
lightning  discharge — billions  of  volts!  (The 
amperage,  of  course,  is  very  low.) 

Wires  are  called  “live”  when  connected  to  a 
source  of  electricity,  even  though  no  current 
flows  in  them.  The  voltage  pressure  is  there 
and  the  current  is  instantly  ready  to  flow  when 
the  circuit  is  closed  or  completed  by  any  means 
whatever.  Live  wires  give  a “shock”  to  the 
person  touching  them  when  the  circuit  is 
closed  by  the  body  and  the  current  flows 
through  it. 


4 


ABOUT  CIRCUITS 


The  Electric  Circuit  Traced  from  the 
Power  Station  Through  a Home 


Diagram  of  a Commercial  Circuit, 
Showing  Various  Sub-circuits 


In  our  reference  to  a circuit  we  have  so  far 
spoken  only  of  a simple  circuit.  In  commercial 
practice,  however,  the  circuits  are  composed  of 
many  sub-circuits.  The  current  that  enters  a 
private  home  is  a sub-circuit,  which  in  its  turn 
also,  is  divided  into  other  sub-circuits. 

The  same  rule  that  applies  to  the  entire  cir- 
cuit, applies  to  any  sub-circuit  or  bypath:  that 
is,  the  circuit  will  only  flow  in  the  bypath  when 
the  conducting  path  is  absolutely  without  any 
break  from  beginning  to  end. 

The  following  interesting  paragraphs  are 
taken  from  Harper’s  Beginning  Electricity  de- 
scribing the  typical  “Electrical  Path.” 

“The  current  leaves  the  generator  at  the 
power  station  in  a steady  flow  and  under  con- 


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EDISON  SCHOOL  OF  SALESMANSHIP 


siderable  pressure.  This  current  travels  over 
an  insulated  wire  out  in  the  street  at  the  rate  of 
186,000  miles  a second.  These  wires,  though  of 
the  best  copper,  offer  some  resistance  to  the 
flow,  and  to  overcome  this  resistance  the  elec- 
tricity loses  some  of  its  voltage,  or  pressure. 

“At  every  point  where  the  wires  are  sus- 
pended from  the  poles  they  must  be  insulated 
with  heavy  glass  or  porcelain  insulators,  or  it 
would  jump  off  and  short  circuit  back  to  the 
power  house. 

“The  current  enters  the  house  over  a copper 
wire  carefully  insulated  with  rubber  and  further 
protected  with  porcelain  tubes  where  it  goes 
through  beams,  walls,  floors,  etc.  This  wire 
leads  it  to  the  watt-hour  meter,  which  de- 
termines how  m,uch  electricity  is  being  used. 
From  the  meter  the  current  flows  along  a copper 
wire,  hidden  away  in  the  walls  of  the  house,  to 
the  electric-lamp  fixture.  Here  it  encounters  an 
incandescent  lamp,  or  even  two  or  three  lamps. 
The  filament  in  the  lamp  is  a very  small  tungsten 
wire,  looped  many  times.  This  wire  is  no  larger 
than  a hair.  It  offers  considerable  resistance 
to  the  passage  of  the  current.  But  there  is 
ample  pressure,  or  voltage,  to  force  the  current 
through  it.  In  overcoming  this  resistance  the 
wire  is  made  white  hot.  All  substances  emit 
light  when  brought  to  a white  heat.  With  some 

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ABOUT  CIRCUITS 


of  its  voltage  lost*  in  overcoming  the  resistance  in 
the  lamp,  or  lamps,  the  current  begins  its  return 
journey. 

“Parallel  with  the  wire  which  conducted  it 
into  the  house  and  through  the  walls  is  another 
copper  wire  of  the  same  size.  This  wire  is  placed 
about  three  inches  from  the  other  wire.  It  is 

also  carefully  insulated The  current 

leaves  the  house  by  this  second  wire,  which  also 
passes  through  the  meter,  and  continues  down 
the  street  over  another  wire  back  to  its  source 
in  the  power  house.” 

It  is  interesting  to  note  that  with  alternating 
current — which  is  most  commonly  used — the 
electricity  reverses  its  direction  of  flow  usually 
every  one  one-hundred-and-twentieth  of  a 
second.  In  other  words,  the  current  would 
flow  over  the  wires  as  just  described  for  1/ 120th 
part  of  a second  and  then  would  flow  back  over 
the  second  wire,  returning  to  the  power  house 
over  the  first  wire,  and  so  on,  making  sixty 
complete  cycles  every  second. 

Open  Circuit 

An  open  circuit  is  a circuit  which  has  a break 
or  gap  in  it,  preventing  the  current  from  flowing. 
A circuit  is  opened,  for  instance,  whenever  the 
electric  current  is  turned  off  by  means  of  a switch. 

*As  a matter  of  fact,  nearly  all  of  its  voltage  is  used  up,  only  enough  remaining  to 
overcome  the  slight  resistance  of  the  return  circuit. 

7 


EDISON  SCIIOOI.  OF  SALESMANSHIP 


A switch  is  a device  by  which  a gap  in  an 
electric  circuit  is  closed  or  opened.  It  has  a con- 
ducting member  which  bridges  or  closes  the  gap 
when  it  is  desired  to  have  the  current  flow. 
When  it  is  desired  to  stop  the  current,  this 
bridge  is  turned  or  moved,  so  as  to  open  the  gap. 


A Knife  Switch 

The  attachment  plug  (on  the  end  of  a flex- 
ible connecting  “cord”),  by  means  of  which  we 
connect  (or  disconnect)  a lamp  or  an  appliance 
to  the  circuit,  is  really  a form  of  switch.  When 
we  unscrew  the  plug  or  pull  it  out,  we  have  made 
the  gap  which  interrupts  the  flow  of  the  current. 

Accidently  opened  circuits  may  be  occasioned 
by  a broken  filament  in  an  incandescent  lamp,  a 
broken  conductor  in  a flexible  cord,  a melted 
fuse,  a break  in  the  wire  composing  the  heating 
element  of  an  appliance  or  any  accidental  break 
in  any  part  of  the  electric  circuit. 

There  are  three  common  troubles  affecting 
an  electric  circuit:  unintentional  open  circuits; 
arcing  which  occurs  accidentally;  short  circuits; 
and  grounded  circuits. 

8 


ABOUT  CIRCUITS 


Arcing 

A break  in  a wire  may  cause  a spark  or  an 
arc.  Two  live  wires  brought  together  and  sep- 
arated slightly  will  make  a spark  or  an  arc,  for 
the  current  will  continue  to  flow  by  jumping 
across  the  gap.  A “spark”  is  simply  the  elec- 
tricity apparent  in  the  air  jumping  a gap.  An 
“arc”  is  produced  when  sufficient  current  is 
flowing  to  cause  the  metal  ends  of  the  conductor, 
not  too  widely  separated,  to  volatilize  and  pro- 
vide a conducting  stream  of  metal  vapor.  It  is 
very  hot. 

In  ordinary  practice,  every  time  a switch  is 
opened,  an  arc  tends  to  form.  This  is  overcome 
by  having  “snap”  or  “quick  break”  switches. 
The  switches  open  so  quickly,  the  arc  is  instan- 
taneously interrupted. 

Arcing  is  a cause  of  trouble  on  flatiron  con- 
tacts; it  also  causes  trouble  at  the  brushes  in 
motors.  On  the  other  hand,  this  phenomenon 
is  the  principle  utilized  in  arc  lam.ps,  which  are 
used  for  street  lighting,  and  in  arc  welding  and 
metal  cutting  and  melting.  (The  temperature 
of  the  arc  in  carbon  arc  lamps  is  about  6000°F.) 

Short  Circuits 

Electricity  always  follows  a path  of  least  re- 
sistance, and  in  branch  circuits  the  current  will 
divide  itself  in  inverse  proportion  to  the  resist- 


9 


EDISON  SCHOOL  OF  SALESMANSHIP 


ance  in  the  various  branches.  Therefore,  if  there 
are  two  branches,  the  branch  which  has  the 
lower  resistance  will  allow  the  most  current  to 
how  through  it. 

If  the  two  wires  of  an  ordinary  household 
circuit  should  come  in  accidental  contact,  a path 
of  very  low  resistance  is  provided  where  they 
touch,  and  the  electricity  in  the  circuit  will  tend 
to  flow  through  this  point  in  preference  to  flow- 
ing through  the  lamps  and  appliances  in  the  cir- 
cuit which  provide  a path  of  comparatively  high 
resistance. 

The  current  would  take  the  shorter  and 
easier  path  and  the  appliances  and  lamps  would 
thus  become  “short-circuited.” 

Of  course  some  current,  even  though  a negli- 
gible amount,  will  continue  to  flow  through  the 
original  circuit,  for  the  current  will  divide  itself 
in  proportion  to  the  conductivity  of  the  various 
paths. 

A short  circuit  might  occur  even  when  the 
wires  do  not  come  actually  together  but  when  a 
metallic  path  of  very  low  resistance  is  provided. 
For  example,  one  might  drop  a screw-driver  ac- 
cidently across  the  two  bare  wires  of  the  circuit, 
and  this  would  have  the  same  effect  as  if  the 
wires  were  actually  in  contact. 

Electric  conductors  must  therefore  be  care- 
fully insulated  from  one  another  by  means  of 


10 


ABOUT  CIRCUITS 


rubber  or  other  insulation,  or  be  supported  by 
insulators  such  as  porcelain  or  glass,  and  guarded 
from  accidental  contact. 


{Illustration  No.  3) 

Accidental  Short  Circuits 


Bare  wires  separated  one  from  another  would 
be  naturally  insulated  by  the  atmosphere  but 
they  would  be  exposed  to  accidental  short 
circuit,  unless  properly  guarded. 

In  practice  we  refer  even  to  partial  short 
circuits  as  short  circuits.  Any  unintentional  or 
accidental  diversion  of  the  current  by  any  means 
is  included  in  the  term  short  circuits,  even  though 
the  short  may  be  of  high  resistance.  A very 
high  resistance  type  of  short  circuit  is  usually 
referred  to  as  a “leak.”  This  is  because  the 
high  resistance  prevents  any  great  amount  of  the 
total  current  flowing  from  being  shorted. 

A very  low  resistance  type  of  short  circuit  is 
usually  referred  to  as  a “dead”  short  circuit,  be- 
cause most  of  the  current  flowing  passes  through 
this  short.  The  word  “dead”  in  this  case  is  only 


II 


EDISON  SCHOOL  OF  SALESMANSHIP 


used  for  emphasis,  as  the  circuit  is  very  m.uch 
“alive”  in  another  sense. 

It  should  be  remembered  that  water  is  also  a 
partial  conductor  of  electricity.  For  that  rea- 
son, conductors  of  electrical  current  are  so  ar- 
ranged that  no  wet  material  will  reach  from  one 
wire  to  the  other. 

For  exam.ple,  take  the  bell-like  shape  of 
nearly  all  insulators  carrying  wires  on  poles. 
These  insulators  are  thus  designed  so  that  when 
it  rains  the  water  drops  from  the  edge  of  the  bell 
and  cannot  form  a continuous  wet  surface  from 
one  wire  to  another. 

A short  circuit  is  real  “trouble”  and  must  be 
repaired  whenever  it  occurs,  to  save  the  current 
going  to  waste,  or  to  insure  all  of  the  current 
passing  through  the  appliance. 

Grounded  Circuits 

Not  only  must  two  conductors  be  kept  in- 
sulated from  each  other,  but  from  the  ground,  or 
earth,  as  well ; for  the  earth  is  a conductor  when 
a good  “ground”  or  contact  is  made. 

When  a conductor  touches  a water-pipe, 
gas-pipe,  lightning  rod,  or  any  other  metal  that 
is  connected  to  moist  earth,  part  of  the  current 
will  be  diverted  through  this  path  to  the  earth, 
provided  the  other  side  of  the  circuit  is  also 


12 


ABOUT  CIRCUITS 


grounded.  The  earth,  with  two  “grounds,” 
makes  a complete  circuit  or  bypath.  See  lower 
drawing  in  illustration  No.  4. 


BATre-ay' 


G/^oa/s/OS 


TO  OtSTA/^T 
TE.UeGRAPH  ST  A 

AAAAAA/' 


CIRCUn  GROUNDED  INTENTIONALLY 


How  Circuits  Are  Grounded 


In  telegraph  circuits,  the  ground  is  utilized 
as  the  return  conductor,  as  shown  in  illustration 
No.  4,  (upper  drawing). 

Different  Kinds  of  Circuits 

There  are  two  kinds  of  circuits:  one  is  the 
series  circuit,  and  the  other  is  the  parallel  or 
multiple  circuit. 


13 


EDISON  SCHOOL  OF  SALESMANSHIP 


The  Series  Circuit 


In  a series  circuit,  exactly  the  same  uniform 
current  flows  through  the  entire  circuit.  This  is 
best  illustrated  in  a diagram. 


Thus  the  current  goes  through  one  lam,p  and 
then  the  other,  and  so  on,  and  the  voltage  or 
pressure,  is  used  up  successively.  If  these  lamps 
are  3^  ampere  and  110  volts  each,  then  the  volt- 
age would  drop  110  volts  in  each  lamp,  or  440 
volts  in  the  series  of  four  lamps.  But  the  same 
3/2  ampere  would  flow  through  them  all. 

This  series  system  of  current  distribution  is 
used  chiefly  in  street  lighting;  in  Xmas  tree 
lighting  sets;  and  in  the  internal  connections  of 
heating  appliances. 

In  a series  circuit,  any  break — as  in  one  of  the 
lamp  filaments  in  the  diagram — interrupts  the 
current  flow  in  the  entire  circuit  and  all  the 
lights  will  go  out.  In  street  lighting  systems, 
special  contrivances  provide  for  the  bridging  of 
the  gap  when  a light  fails,  so  as  not  to  have  all 
the  lights  on  the  circuit  go  out. 


14 


ABOUT  CIRCUITS 


How  Various  Heats  Are  Obtained 

Nearly  all  two  or  three-heat  appliances  have 
two  complete  heating  coils  or  sets  of  coils.  The 
low  “heat”  is  obtained  by  connecting  these  sets 
of  coils  in  series. 


B 

medium  meat  : on^ 

one  coil  Set  in  use. 


A 


{Illustration  No.  6) 


Diagram  of  Wiring  in  a Three-heat  Hotpoint  Grill* 

As  shown  in  the  above  diagram  A,  of  a three- 
heat  grill,  to  get  low  heat,  the  current  must  first 
go  through  one  set  of  coils  and  then  through  the 
other.  The  effect  is  to  double  the  length  of  the 
resistance  wire,  or  to  double  the  resistance  of  the 
circuit. 

The  total  resistance  of  a series  circuit  is  equal 
to  the  sum  of  its  farts. 

In  a 600-watt,  100  volt  grill  each  of  the  two 
sets  of  coils  consumes  one-half  of  the  watts  or 
300  watts.  Therefore,  each  has  a resistance  of 


*For  simplicity  the  diagram  shows  but  two  coils.  Actually  in  a Hotpoint  grill 
there  are  eight  coils — four  in  each  set. 


15 


EDISON  SCHOOL  OF  SALESMANSHIP 


When  both  sets  of  coils  are  joined  in  series, 
and  the  grill  is  connected  to  a 100  volt  circuit, 
the  current  has  to  flow  over  twice  33  ohms,  or 

66  ohms  and  therefore  only  or  amperes 


will  flow.  (V-j-0=A).  Consequently  only  100x13^ 
or  150  watts  will  be  consumed.  (V  x A =W). 
Note  that  150  watts  is  3^  of  600  watts.  There- 
fore with  both  sets  of  coils  switched  on  in  series 
the  appliance  is  generating  low  heat. 


Now  in  order  to  secure  a medium  heat,  one 
of  the  sets  of  coils  is  cut  out  (not  used)  so  that 
the  current  flows  through  only  one  set.  (Dia- 
gram B,  see  previous  page.)  This  in  effect 
reduces  the  resistance  one-half  and  more  current 
flows  and  more  heat  is  generated. 

The  method  that  produces  high  heat  is  ex- 
plained in  detail  in  the  second  section  following 
under  the  heading  “The  Parallel  or  Multiple 
Circuit.” 


Voltage  Drop 


In  considering  voltage  drop  think  what 
electricity  does  in  a circuit.  THE  WORK 
OF  ELECTRICITY  IS  OVERCOMING 
RESISTANCE.  In  fact,  work  of  all  kinds  is 
the  overcoming  of  resistance. 

16 


ABOUT  CIRCUITS 


There  are  two  forms  of  resistance  in  electric 
circuits : 

1st — Resistance  which  is  a quality  of  the  con- 
ductor itself,  and  which  varies  directly  as  the 
length  and  inversely  as  the  cross  section  of  the 
conductor. 

2d — Resistance  due  to  a back  pressure  or 
counter-voltage  which  develops  in  electromag- 
netic apparatus  such  as  motors  and  transformers. 

Work  is  done  in  overcoming  either  or  both  of 
these  above  forms.  In  overcoming  resistance  in 
any  circuit,  it  is  the  electromotive  force  or  the 
voltage  pressure  that  is  used  up  and  not  the 
amperage  or  the  current.  For  instance,  when 
a current  of  one  ampere  under  a pressure  of  100 
volts  is  sent  from  a battery  or  dynamo  out  over 
a wire  to  do  useful  work  it  returns,  after  its  work 
is  completed,  to  the  generator,  still  with  a cur- 
rent strength  of  one  ampere  but  with  no  pres- 
sure or  force.  It  has  suffered  a drop  in  voltage 
because  of  the  work  done. 

Rule  : The  voltage  drop  is  proportional  to  the 
resistance  overcome. 

Let  us  illustrate  this  by  a water  motor  at- 
tached to  a faucet.  The  stream  of  water  that 
comes  out  of  the  motor  is  the  same  stream  that 
goes  in;  it  has  the  same  flow  in  gallons  per  hour 


17 


EDISON  SCHOOL  OF  SALESMANSHIP 


but  it  has  lost  its  pressure  or  “live”  force.  It 
goes  in  perhaps  at  a pressure  of  50  pounds  per 
square  inch  and  com,es  out  at  a pressure  of  10,  5, 
or  perhaps  0 pounds,  depending  on  the  power 
used  by  the  m.otor. 

Rule  : Voltage  drop  also  is  proportional  to  the 
current  flowing. 

For  if  it  takes  100  volts  to  force  2 amperes 
through  a circuit  of  50  ohm.s,  the  voltage  drop  is 
100  volts;  then  obviously  it  will  take  double  the 
volts  to  force  4 amperes  through  the  same  circuit, 
and  the  voltage  drop  will  be  200  volts. 

We  may  cofnbine  the  two  foregoing  rules  and 
state:  The  voltage  drop  is  proportional  both  to  the 
resistance  and  the  current. 

These  principles  are  illustrated  in  the  fol- 
lowing diagram  of  a series  circuit  consisting  of  5 
lamps,  each  having  a resistance  of  40  ohms,  and 
2 heaters,  each  with  15  ohms  resistance.  There 
are  2 amperes  flowing. 


{Illustration  No.  7) 

Showing  Voltage  Drop  Through  Lamps  and  Heaters 
In  Series 


18 


ABOUT  CIRCUITS 


The  following  examples  show  how  the  total 
resistance  is  found;  how  the  voltage  drop  and 
the  wattage  consumption  is  determined. 


5 lamps,  40  ohms 

= 

200  ohms 

2 heaters,  15  ohms.  . . . 

= 

30  ohms 

Circuit  Wires,  1 ohm,  . . 

= 

1 ohm 

Total  Resistance  . . . 

231  ohms 

Ohms  X 

Amp.  = Volts 

Drop  due  to  lamps  .... 

200  X 

2 = 400 

Drop  due  to  heaters . . . 

30  X 

2 = 60 

Drop  due  to  wires 

1 X 

2 = 2 

Voltage  Drop  (total) 

231  X 

2 = 462 

Volts  X Amp.  = Watts 

Watts  used  in  lamps  . . 

400  X 

2 = 800 

Watts  used  in  heaters 

60  X 

2 = 120 

Watts  used  in  wires.  . 

2 X 

2=4 

Total  Watts  used  . . 

462  X 

2 = 924 

In  our  example  (page  15)  of  the  three-heat 
grill,  with  two  sets  of  coils  in  series,  having  a 
total  resistance  of  66  ohms,  each  set  having  33 
ohms,  the  voltage  drop  will  be  50  volts  in  each  set. 

Closely  associated  with  voltage  drop  is 
energy  loss.  It  is  measured  in  watts,  and  is  the 
product  of  the  voltage  drop  multiplied  by  the 
amperes  flowing. 

The  relation  between  volts  used  up  and  watts 
(or  energy)  used  up  is  shown  in  the  foregoing 
examples. 


19 


EDISON  SCHOOL  OF  SALESMANSHIP 


The  energy  loss  in  watts  may  also  be  com- 
puted directly  from  the  current  because  it  varies 
as  the  square  of  the  amperes  flowing  multiplied 
by  the  ohms  resistance  of  the  circuit  or  part 
of  the  circuit  in  question.  This  follows  from  the 
fact  that  W =VxA  and  V =AxO.  Therefore 
substituting  the  equivalent  of  V,  which  is  A x 0, 
into  the  formula  W =V  x A,  we  have  Watts  = 
A X O X A =A^O. 

This  is  also  apparent  from  the  example  on 
the  preceding  page:  924  watts  is  seen  to  be  the 
product  of  the  ohms  (231)  times  the  amperes 
taken  twice  (2  times  2). 

The  Parallel  or  Multiple  Circuit 

In  this  form  of  circuit,  the  current  flows  in 
parallel  branches,  or  in  a multiple  of  branches 
or  bypaths  and  the  current  divides  itself  into  these 
bypaths  or  branches  in  proportion  to  their  relative 
conductivity,  or,  to  put  it  the  other  way  around, 
the  current  divides  in  inverse  proportion  to  their 
relative  resistance. 

Consider  a two  branch  circuit  of  equal  con- 
ductivity or  resistance.  The  two  sets  of  coils  in 
a grill,  as  in  most  “three-heat”  appliances,  make 
a good  example.  The  diagram  on  the  opposite 
page  shows  the  coils  in  parallel,  or  multiple, 
as  connected  for  high  heat. 


20 


ABOUT  CIRCUITS 


WwwV 


HIGti  MEAT  : both  sets 
of  Coils  in  use  in  par- 
ollel. 

{Illustration  No.  8) 

The  Diagram  Shows  the  Wiring  Method,  and  Path  of  the 
Current  for  High  Heat  in  a Hotpoint 
Grill  Heating  Unit 

{Compare  illustration  No.  6) 

In  this  case  it  is  easier  for  the  current  to  flow 
in  two  paths  than  in  one,  in  fact,  it  is  twice  as 
easy.  This  is  equivalent  to  doubling  the  area  of 
the  cross  section  of  one  of  the  coils,  which  could 
be  done  by  twisting  the  wires  tightly  together 
and  into  one  cable.  The  result  would  be  a wire 


33 


or 


16.5 


or  cable  which  would  make  a coil  of  - 
ohms.  ^ 

Putting  it  another  way,  each  coil  or  set  of  coils 

in  the  grill  carries  -jy  =3.3  amperes,  for  amperes  = 

voltage  Therefore  the  two  sets  of  coils  carry 
resistance 

6.6  amperes  or  660  watts,  for  watts  equal  the 
voltage  multiplied  by  the  amperage. 

Let  us  see  how.  Neglecting  the  voltage  drop 
in  the  leads  or  wiring  to  the  grill,  and  assuming 
the  voltage  at  the  grill  to  be  exactly  100,  then 
each  “coil”  is  so  connected  that  each  receives  100 


21 


EDISON  SCHOOL  OF  SALESMANSHIP 


volts  pressure  and  there  is  a voltage  drop  of  100 
in  each;  and  as  each  coil  has  a resistance  of  33 
ohms,  a current  of  3.3  amperes  will  flow  through 
each  one  at  the  same  time;  so  there  will  be  a total 
of  6.6  am.peres,  or  660  watts. 

(If  the  sets  of  coils  were  connected  in  series, 
the  voltage  drop  would  be  50  in  each  coil  and,  as 
we  have  seen,  only  1.65  amperes  would  flow — 
first  through  one  coil  and  then  the  other.) 

Rule  : In  a multiple  {or  parallel)  circuit  of 
two  branches,  each  having  equal  resistance  or  con- 
ductivity, the  combined  conductivity  of  the  circuit 
is  double  and  the  combined  resistance-  is  one-half. 

In  a multiple  circuit  of  three  branches  of  equal 
resistance  or  conductivity,  the  combined  conduc- 
tivity is  trebled  and  the  resistance  is  one-third. 

Corresponding  rules  apply  to  multiple  cir- 
cuits of  various  numbers  of  branches  of  equal 
resistance. 


A Multiple  Circuit  with  Two  Branches  of 
Unequal  Resistance 

In  multiple  circuits  with  branches  of  unequal 
resistance,  analysis  is  more  complicated  and  the 


22 


ABOUT  CIRCUITS 


full  explanation  lies  outside  the  scope  of  this 
course;  but  one  example  may  be  given. 

Let  us  suppose  a parallel  circuit  as  illustrated. 
Branch  “B”  has  twice  the  resistance  of  “A”  and 
therefore  one-half  the  conductivity.  Let  “A” 
have  5 ohms  and  “B”  10  ohms,  and  the  voltage 

drop  100  volts.  Then  = 20  amperes  will 

flow  in  “A”  and  = 10  amperes  will  flow  in 

“B”;  and  30  amperes  will  flow  in  both.  The 
combined  resistance  is  equal  to  the  voltage  di- 
vided by  the  combined  current:  =3.3  ohms. 

If  both  branches  were  5 ohms  each,  the  result 
would  be  2.5  ohm,s;  if  10  ohms  each,  it  would  be 
5 ohms. 

Distribution  Systems 

The  illustration  on  page  5,  which  is  a dia- 
gram of  a distributing  circuit  of  a power  house 
or  central  station,  is  of  course  a multiple  circuit 
of  many  branches. 

In  cities  and  towns  there  are  usually  four  im- 
portant major  circuits  going  out  from  the  power 
house  or  central  station. 

First'.  Street  lighting  such  as  arc  or  in- 
candescent lamps. 

This  is  a series  circuit.  The  voltage  depends 


23 


EDISON  S C II  O O I,  OF  SALESMANSHIP 


on  the  number  of  lamps  in  series  up  to  approx- 
imately 2000  volts. 

Second:  The  trolley  or  street-car  power  cir- 
cuit. 

This  is  usually  a 500  or  600  volt  circuit  of 
direct  current,  as  street-car  motors  are  direct 
current  motors. 

Third:  Power  circuit  which  supplies  the 
power  load  of  motors  in  factories. 

Usually  it  is  220  or  440  volts. 

Fourth:  Incandescent  lighting  circuit  used 
in  homes  and  buildings. 

This  is  a 110  volt  circuit.  (See  section  on 
three-wire  distribution,  following.) 


The  Current  in  the  Trolley  Wire  Flows  Down  the  Trolley  Pole 
Through  the  Motor,  Through  the  Wheels  to  the 
Track  and  Back  to  the  Generator 

The  voltages  referred  to  above  are  used  in 
local  circuits.  These  circuits  are  fed  by  high 
tension  feeders  from  the  power  house  carrying 
a current  of  higher  voltage  which  is  reduced  to 
the  required  voltage  by  transformers. 


24 


ABOUT  CIRCUITS 


Telegraph,  telephone,  burglar  alarm  and  fire 
alarm  circuits  are  not  part  of  the  Central  Sta- 
tion Distribution  System. 

These  are  low  voltage  circuits  supplied  from 
batteries  or  low  voltage  dynamos,  although  the 
Central  Station  may  in  some  cases  furnish  the 
electricity  to  supply  storage  batteries  or  to 
operate  motors  which  drive  these  low  voltage 
generators. 

To  prevent  voltage  drop  in  a distribution  sys- 
tem the  main  branches,  lines  and  feeders  carry- 
ing the  current  to  the  sub-circuits  are  made  large 
enough  and  with  sufficiently  low  resistance  to 
prevent  any  serious  voltage  drop.  This  in  order: 

1st — To  maintain  the  proper  voltage  in 
homes  and  buildings  no  matter  how  many 
lights  or  appliances  are  turned  on. 

2d — ^To  prevent  a waste  of  electrical  energy, 
which  the  voltage  drop  multiplied  by  the  current 
represents. 


A Sub-branch  Multiple  Circuit 

The  Central  Station  or  light  company  is  not 
responsible  for  the  wiring  within  a building.  Of 


25 


EDISON  SC  HOOT,  OF  SALESMANSHIP 


course,  the  wires  should  be  sufficiently  large  to 
carry  the  current  required. 

Every  time  a switch  is  turned  on  in  a mul- 
tiple circuit,  it  provides  another  bypath,  and 
allows  more  current  to  flow  in  the  main  circuit, 
for  each  additional  lamp  burning  requires  an 
additional  3^  ampere  and  a flatiron  5 or  6 
amperes. 

The  resistance  of  the  multiple  sub-circuits 
varies  inversely  according  to  the  number  of  ap- 
pliances in  use;  i.  e.,  their  total  resistance. 

(The  resistance  of  the  main  leads  and  feeders, 
of  course,  is  in  series  with  the  sub-branch  cir- 
cuits and  is  constant.) 

The  voltage  drop,  as  we  have  learned,  varies 
with  the  current  flowing.  When  the  current  is 
increased  in  the  main  leads  and  feeders,  more 
voltage  is  required  to  force  the  current  through 
the  wires  and  overcome  their  resistance;  there- 
fore the  greater  the  current  the  greater  the 
voltage  drop. 

There  is,  of  course,  a practical  limit  to  the 
size  of  conductors  used  for  mains  and  feeders, 
which  is  determined  by  their  cost  and  the  interest 
charge  on  the  investment. 

In  cities  and  towns  a voltage  drop  of  5%  is 
usually  allowed.  In  long,  high  voltage  trans- 
mission lines  a very  much  larger  drop  is  allowed. 


26 


ABOUT  CIRCUITS 


This  brings  up  a very  important  point  in  the 
transmission  of  power,  the  advantages  of  high 
voltage  for  transmission. 


Modern  Steel  Towers  Carrying  High  Tension  Electricity 
Across  Country 

Power  is  the  product  of  V x A.  The  voltage 
of  transmission  does  not  depend  on  the  size  of 
the  wire,  although  the  current  does.  (The  volt- 
age which  may  be  transmitted  depends  on  the 
insulation  used.)  One  KW  or  100  KW  may  be 
transmitted  over  the  same  wire,  provided  it  is 
properly  insulated!  At  100  volts,  10  amperes 
will  produce  1 KW.  At  10,000  volts,  10  am- 
peres will  produce  100  times  as  much,  or  lOOKW. 
But  the  same  wire  properly  insulated  will  carry 
either.  That  is,  with  the  same  loss  or  voltage 
drop  in  transmitting.  If  we  allow  5 volts  drop 
in  the  first  case,  950  watts  will  be  delivered,  or 
5%  lost.  In  the  second  case,  with  5 volts  drop, 
99,950  watts  will  be  delivered,  or  only  .005%  lost! 

Alternating  current  can  be  easily  transformed 


27 


EDISON  SCHOOL  OF  SALESMANSHIP 


by  means  of  transformers  from  one  voltage  to 
another,  up  or  down,  and  is  generally  used  in 
transmitting  power  over  distances  of  a mile  or 
so.  In  fact,  it  is  superseding  direct  current 
almost  entirely  for  lighting  and  power.  It  is  not 
uncommon  to  transmit  electric  power  over  long 
distances  at  100,000  volts  or  more. 


Three-wire  System 

There  is  another  way  in  which  the  cost  of  a 
local  distribution  system  can  be  reduced  and  that 
is  by  the  three-wire  system  introduced  by  Edison. 


{Illustration  No.  13) 


A Simple  Three-wire  System 


For  example:  Two  110  volt  dynamos  or  gen- 
erators are  connected  in  series  so  the  voltage 
between  the  outside  wires  “A”  and  “C”  is  220  V. 
Yet  the  system  provides  for  110  volt  service  in 
the  homes  and  the  use  of  110  volt  lamps  and 
appliances. 

If  the  two  “sides”  are  perfectly  balanced, 
both  have  the  same  resistance,  and  no  current 
will  flow  back  to  the  generators  through  “B;” 
and  “B,”  which  is  the  middle  or  neutral  wire. 


28 


ABOUT  CIRCUITS 


has  only  to  be  large  enough  to  carry  the 
unbalanced  current. 

“A”  and  “C”  only  carry  a current  equal  to 
one-half  that  required  to  supply  the  same  num- 
ber of  lamps  and  appliances  in  two  ordinary  110 
volt  multiple  two-wire  circuits.  So,  a great  sav- 
ing in  conductors  m,ay  be  made. 

It  is  a combination  series-multiple  circuit.  It 
has  practically  the  advantage  of  a 220  volt  mul- 
tiple system.,  and  the  effect  is  accom.plished  by 
placing  one  group  of  110  volt  lamps  and  appli- 
ances in  series  with  another  group  of  110  volt 
lamps  and  appliances. 

When  the  load  on  each  side  is  balanced  “B” 
serves  merely  as  a “bus,”  that  is,  a comm,on  con- 
nector between  the  lamps  on  one  side  and  those 
on  the  other,  connecting  them  in  series.  If  there 
is  a difference  in  the  loads,  then  “B”  will  carry 
the  difference. 

In  most  cities  and  towns  alternating  current 
is  generated  and  distributed  at  2300  volts  to  the 


{Illustration  No.  14) 

Diagram  of  High  T ension  Wiring  with  Step  Down  Transformer, 
Enabling  Use  of  High  Voltage  Generator  and 
Low  Voltage  Secondary  Circuits 


29 


EDISON  SCHOOL  OF  SALESMANSHIP 


various  centers  of  distribution,  usually  on  each 
block,  where  transformers  step  it  down  to  110 
and  220  volts  for  distribution  to  the  various 
houses  and  buildings  on  the  block,  over  local 
1 10-220  volt  three  -wire  circuits. 

Electricity  and  the  Human  Body 

The  resistance  of  the  body  to  the  passage  of 
electric  current  may  be  as  much  as  100,000  ohms. 
This  resistance  is  chiefly  in  the  outer  skin. 

The  dry  hands  of  a workman  whose  skin  is 
tough  and  horny  have  many  times  the  resist- 
ance of  the  moist  hands  of  a person  whose  skin 
is  thin  and  tender. 

One  cannot  feel  the  current,  for  example, 
from  an  ordinary  battery  or  dry  cell,  because  the 
cell  has  only  l^^  volt  pressure  and  assuming  the 
resistance  of  the  body  to  be  100,000  ohms  it  is 
evident  that  only  \}/2  millionths  of  an  ampere 
can  flow,  which  is  not  enough  to  produce  sen- 
sation. 

If  the  wires  from  a dry  cell  are  placed  to  the 
tip  of  .the  tongue  the  current  can  be  felt  slightly. 
In  this  case  the  resistance  through  the  tongue 
might  be  about  1500  ohms,  and  therefore  one 
thousandth  part  of  an  ampere  would  flow. 

If  the  two  conductors  of  a 110  volt  circuit  are 
touched  with  dry  Angers,  probably  one  thou- 
sandth of  an  ampere  will  flow,  which  would 


30 


ABOUT  CIRCUITS 


hardly  be  felt.  If  the  fingers  are  moistened  and 
the  conductors  touched,  a slight  shock  and  a 
twitching  of  the  muscles  may  be  felt. 

Severe  high  voltage  shocks  produce  uncon- 
sciousness similar  to  drowning,  and  the  person 
usually  can  be  resuscitated  if  properly  treated  in 
time,  although  heart  failure  may  result. 

Body  shock  then,  depends  upon  the  number 
of  amperes  which  are  forced  through  the  body, 
and  not  directly  upon  the  voltage.  A heavy 
current  also  produces  bad  burns. 

The  sparks  which  come  from  a comb  on  a cold 
day  when  combing  the  hair  may  be  1000  volts; 
the  sparks  from  a rapidly  moving  leather  belt 
may  be  50,000  volts  or  more,  but  the  momentary 
current  flowing  in  each  case  is  inflnitesim,al  and 
therefore  perfectly  harmless.  There  is  no  danger 
then  in  the  ordinary  house  circuit,  under  ordi- 
nary circumstances. 

Persons  have  been  shocked  beyond  resusci- 
tation by  standing  in  a bathtub  and  touching 
the  metal  part  of  an  improperly  insulated  elec- 
tric light  socket.  In  this  case  there  was  a 
“ground”  on  the  circuit  and  the  body  made 
connection  complete  from  the  socket  through  the 
body  to  the  water  to  the  water  pipes  to  the  earth 
and  then  to  the  other  leak  or  “ground.”  (See 
page  13  about  grounds  on  both  sides  of  the 
circuit.) 


31 


